Table 1 Histiogenic Classification and Metastatic Potential of Canine Soft Tissue Sarcomas Tissue of Origin Benign Malignant Primary Sites

Soft Tissue Sarcomas Incidence and Risk Factors Soft tissue sarcomas are a heterogeneous population of mesenchymal tumours representing 15% of skin and subcutaneous tumours in the dog and 7% in the cat. Sarcomas have been associated with radiation, trauma, foreign bodies, orthopaedic implants, subcutaneous infections, including vaccines, and the parasite Spirocerca lupi. Most soft tissue sarcomas are solitary tumours which tend to be seen in middle-aged to older dogs, with a median age of 10 years (range 5 17 years), and tend to be seen in medium to large breed dogs, with no specific breed or sex predilection for soft tissue sarcomas except for synovial cell sarcomas in large breed dogs and the occurrence of rhabdomyosarcoma in young dogs. Tumour Pathology and Biological Behaviour Soft tissue sarcomas are a heterogeneous group of tumours with a similar pathologic appearance and clinical behaviour. They are often grouped together as their histological classification and differentiation is complicated. Sarcomas arise from mesenchymal tissues and generally have features similar to the cell type of origin, depending on the grade (Table 1). These tumours originate in connective tissues, including muscle, adipose, neurovascular, fascial, and fibrous tissue, and can give rise to benign and malignant entities. Only malignant soft tissue sarcomas will be covered here. Malignant neoplasms in this category include fibrosarcoma, peripheral nerve sheath tumour (PNST; or malignant schwannoma, neurofibrosarcoma, or haemangiopericytoma), myxosarcoma, undifferentiated sarcoma, liposarcoma, malignant fibrous histiocytoma, and rhabdomyosarcoma (Table 2). The term soft tissue sarcoma generally excludes those tumours of haematopoietic or lymphoid origin, and haemangiosarcoma (although the dermal form is considered here), mast cell sarcoma, oral sarcoma, osteosarcoma, and chondrosarcoma are also not covered. Tumours listed as Soft tissue sarcoma have similar biologic behaviour characterized by local invasion and a lowto-moderate metastatic potential. Tumours listed under Other soft tissue sarcoma are atypical because of a different location (e.g. leiomyosarcoma and synovial cell sarcoma) or higher metastatic rate (leiomyosarcoma, rhabdomyosarcoma, lymphangiosarcoma and synovial cell sarcoma). Some sarcomas not considered as soft tissue sarcomas are considered briefly because of similarities in location to other soft tissue sarcomas (e.g., histiocytic sarcoma and dermal haemangiosarcoma). Soft tissue sarcomas may arise from any anatomic site in the body, although skin and subcutaneous sites are most common. Soft tissue sarcomas have the following important common features with regard to their biologic behaviour: They appear as pseudoencapsulated soft-to-firm tumours but have poorly defined histologic margins or infiltrate through and along fascial planes, and are locally invasive. Local recurrence after conservative surgical excision is common. Sarcomas tend to metastasize haematogenously, in up to 20% of cases. Regional lymph node metastasis is unusual (except for synovial cell sarcoma). Histopathological grade is predictive of metastasis, an Assessment of the margins of excision is predictive of local recurrence. Measurable or bulky (>5 cm in diameter) tumours generally have a poor response to chemotherapy and radiation therapy (RT). Skeletal muscle Rhabdomyoma Rhabdomyosarcoma Tongue, larynx, heart, and urinary bladder Table 1 Histiogenic Classification and Metastatic Potential of Canine Soft Tissue Sarcomas Tissue of Origin Benign Malignant Primary Sites Metastatic Potential Metastatic Sites Fibrous tissue Fibroma Fibrosarcoma Extremity and oral Low-tomoderate* Lungs cavity Nervous tissue Peripheral nerve Extremity Low-tomoderate* Lungs sheath tumour Myxomatous Myxoma Myxosarcoma Extremity and Low-tomoderate Lungs tissue joints Adipose tissue Lipoma Liposarcoma Extremity and ventrum ± abdominal or thoracic cavity Low-tomoderate Lungs ± liver, spleen, bone Low-tomoderate Lungs ± liver, spleen, kidneys Smooth muscle Leiomyoma Leiomyosarcoma Gastrointestinal ± Moderate Lymph nodes, Staffordshire & Derbyshire Clinical Club 9 th May 2018 1

spleen, liver, vulva and vagina, and subcutaneous tissue Synovial tissue Synovioma Synovial cell sarcoma Joints Moderateto-high (according to grade)* Histiocytic cells Histiocytoma Histiocytic sarcoma Extremity Moderateto-high liver ± spleen, kidneys, peritoneum Lymph nodes and lungs Lymph nodes ± lungs, spleen, liver, kidneys Lymph vessels Lymphangioma Lymphangiosarcoma Extremity Moderate Lymph nodes Blood vessels Haemangioma Haemangiosarcoma Spleen, heart, liver ± skin, muscle, bone, kidneys, and retroperitoneum Table 2. Types of Soft Tissue Sarcoma Type of Sarcoma Tumours Soft tissue sarcoma Fibrosarcoma PNST* Liposarcoma Myxosarcoma Malignant mesenchymoma Other soft tissue sarcoma Leiomyosarcoma (Atypical soft tissue sarcoma) Rhabdomyosarcoma Synovial cell sarcoma Lymphangiosarcoma Non soft tissue sarcoma Histiocytic sarcoma Haemangiosarcoma Osteosarcoma Chondrosarcoma Melanoma Lymphoma High Lungs, liver, lymph nodes, distant dermal sites Many of these tumours have histologic patterns with overlapping features within a group and between groups with different histogenesis. In addition, the histologic nomenclature for some sarcomas may vary from pathologist to pathologist. The development of immunohistochemistry has improved diagnosis of soft tissue sarcomas in veterinary pathology, but this still remains imperfect. Before a management plan can be made, it is necessary to know the histologic type, size, site, and grade of the tumour and the stage of disease. Histologic grading (e.g., low, intermediate, or high or I, II, III) is assigned after histologic characterization from adequate biopsy specimens (Table 3). Table 3. Soft Tissue Sarcoma Grading System Score Differentiation Mitosis Mitoses/10 hpf Necrosis 1 Resembles normal adult mesenchymal tissue 0-9 None 2 Specific histologic subtype 10-19 <50% necrosis 3 Undifferentiated >20 >50% necrosis Grade I: Cumulative score of 4 for the three categories. Grade II: Cumulative score of 5-6. Grade III: Cumulative score of 7. History and Clinical Signs Soft tissue sarcomas generally present as a slow growing mass anywhere in the body. Rapid tumour growth, intratumoural haemorrhage, or necrosis can be seen in some cases. The clinical signs depend of the location and invasiveness of the tumour, with the exception of tumour hypoglycaemia in smooth muscle tumours. Tumours may vary in clinical characteristics, but they are usually firm and adherent (fixed) to skin, fascia, muscle, or bone. They may be soft and lobulated, mimicking lipomas. Intra-abdominal tumours often compress the GI or urogenital tracts and patients may present with vomiting, diarrhoea, melena, dyschezia or dysuria. Local invasion may cause melaena, vulval bleeding or haematuria. PNSTs, involving the brachial or lumbosacral plexus, usually result in pain, lameness, muscle atrophy, and eventual paralysis. These tumours are generally located axially and therefore difficult to palpate, making early diagnosis difficult. Staffordshire & Derbyshire Clinical Club 9 th May 2018 2

Diagnostic Techniques and Work-Up Diagnostic tests performed for diagnosis and clinical staging depend on the type of soft tissue sarcoma, especially with atypical forms (e.g., HSA, histiocytic sarcomas, lymphangiosarcomas and synovial cell sarcomas), but comprise tumour FNA or biopsy, lymph node FNA or biopsy, routine haematological and biochemical screens, thoracic radiographs, abdominal ultrasonography, and regional imaging of the tumour for planning surgery or RT. Fine-needle aspiration (FNA) is recommended to exclude other differential diagnoses, but this may not be sufficient for a definitive diagnosis because false-negative results can occur due to poor exfoliation of cells in comparison to epithelial and round cell tumours, or due to the presence of tumour necrosis. In one study of 40 dogs, 15% of dogs were incorrectly diagnosed and a further 23% of samples were non-diagnostic. Biopsy methods for definitive preoperative diagnosis of soft tissue sarcomas include needle-core, punch, incisional, or excisional biopsies. The biopsy should be planned and positioned so that the biopsy tract can be included in the curative-intent treatment without increasing the surgical dose or size of the radiation field. Excisional biopsies are not recommended because they are rarely curative and the subsequent surgery required to achieve complete histologic margins is usually more aggressive than surgery following core or incisional biopsies, resulting in additional morbidity and treatment costs. Multiple attempts at resection, including excisional biopsy, prior to definitive therapy have a negative impact on survival time in dogs with soft tissue sarcomas. Despite the low incidence of lymph node metastasis for many sarcomas, a FNA or biopsy of the regional lymph nodes is indicated if they are clinically abnormal, if the tumour is high-grade (III) or if the tumour is an atypical soft tissue sarcomas with a high rate of metastasis to regional lymph nodes, such as HSA, histiocytic sarcomas, lymphangiosarcoma, synovial cell sarcoma, leiomyosarcoma, and possibly rhabdomyosarcoma. Routine blood screen are usually unremarkable, apart from haematological abnormalities such as anaemia and thrombocytopenia in dogs with disseminated histiocytic sarcomas and HSA, and hypoglycaemia in dogs with intraabdominal smooth muscle tumours. Three-view thoracic radiographs should be performed prior to definitive treatment because the lungs are the most common metastatic site for typical soft tissue sarcomas. Abdominal imaging is recommended for the assessment of metastasis to intra-abdominal organs, especially the lymph nodes, spleen, and liver, in animals with suspected intra-abdominal neoplasia (e.g. GI leiomyosarcoma or splenic sarcoma) or advanced stage and high-grade pelvic limb soft tissue sarcoma. Clinical Staging A modified staging system (Table 3) has been described for soft tissue sarcomas in dogs, which has less emphasis on tumour size, which is an arbitrary assignment, and greater emphasis on depth of invasion, which has more biological relevance. A superficial tumour is defined as a soft tissue sarcoma located above the superficial fascia and that does not invade the fascia, whereas a deep tumour is located deep to the superficial fascia, invades the fascia, or both. The stage grouping takes into account both clinical staging criteria (TNM staging system) and histological grade. Table 3 Modified Staging System for Soft Tissue Sarcomas T Primary tumour Tx Primary tumour cannot be assessed T0 No evidence of primary tumour T1 Tumour <5cm in greatest dimension, (a) superficial tumour, (b) deep tumour T2 Tumour >5cm in greatest dimension, (a) superficial tumour, (b) deep tumour N Regional lymph node Nx Regional lymph nodes cannot be assessed N0 No regional lymph node metastasis N1 Regional lymph node metastasis M Distant metastasis Mx Distant metastasis cannot be assessed M0 No distant metastasis M1 Distant metastasis G Histologic grade Gx Grade cannot be assessed G1 Low (grade I) G2 Intermediate (grade II) G3 High (Grade III) Stage I G1 2 Any T N0 M0 II G3 T1a-b, T2a N0 M0 Staffordshire & Derbyshire Clinical Club 9 th May 2018 3

III G3 T2b N0 M0 IV Any G Any T N1 Any M Any G Any T Any N M1 Treatment The biological behaviour of most tumours in this heterogeneous group is typified by local invasion, with a low to moderate rate of metastasis, and the treatment plan should taken account of this. Local tumour control is the most important consideration in the management of soft tissue sarcomas and surgical resection is the main treatment for dogs with soft tissue sarcomas. RT also plays an important role in local tumour control, especially for incompletely resected and unresectable soft tissue sarcomas. However, definitive treatment options depend on histologic subtype (especially for atypical soft tissue sarcomas such as HSAs, histiocytic sarcomas, and lymphangiosarcomas), tumour location, clinical stage, histologic grade, and completeness of surgical margins. A strategy for managing dogs with typical soft tissue sarcomas is presented below. 1. Biopsy confirms soft tissue sarcoma (and ideally grade) 2. Radical local surgery is performed 3. If margins are complete, further management is dependent on grade: a. Grade I/II: Active clinical monitoring of the surgical site b. Grade III: Consider adjuvant chemotherapy with doxorubicin-based protocol 4. If margins are incomplete, further management is indicated a. Active surveillance of the surgical site b. A staging excision to identify whether tumour cells are present in the wound i. If tumour is present, a wider excision is performed ii. If tumour is not present, active monitoring may be performed c. Wider surgical excision of the surgical scar d. Radiotherapy e. Adjuvant metronomic chemotherapy f. If the tumour is grade III, consider adjuvant chemotherapy Surgery Soft tissue sarcomas are locally aggressive tumours that grow along paths of least resistance and invade surrounding tissue, resulting in the formation of a pseudocapsule of compressed viable tumour cells, which gives the false impression of a well-encapsulated tumour. However, surgical removal without adequate margins will result in incomplete excision and a high risk of local tumour recurrence. The first surgery provides the best opportunity for local tumour control as the management of incompletely resected tumours increases patient morbidity and treatment costs, increases the risk of further local tumour recurrences, and decreases survival time. The minimum recommended margins for surgical resection are 3 cm lateral to the tumour and one fascial layer deep to the tumour, to include any biopsy tracts and areas of fixation to surrounding tissue, e.g. bone and fascia, en bloc with the tumour. Procedures with margins less than 2cm may be considered as incomplete, even if macroscopic tumour is not detected at the plane of excision. If the tumour is attached to a muscle or fascial plane, the entire anatomical layer has to be removed. Fat and loose connective tissues do not function as good tumour barriers, necessitating wide margins. Tumours should not be shelled out of their pseudocapsule due to the high risk of regrowth of remaining tumour cells remaining in and beyond the capsule. Radical surgery such as limb amputation or hemipelvectomy may be required to achieve adequate surgical margins and local tumour control. Alternatively, planned cytoreductive surgery and postoperative RT may be limb sparing and reduce patient morbidity. Since relatively few dogs die of tumour-related causes, radical resection of sarcomas on the limbs should be perhaps considered as a last resort for recurrent and high grade tumours. The resected tumour should be pinned out, e.g. on card, to the original dimensions to prevent shrinkage during formalin fixation and the lateral and deep margins may be inked to aid in histologic identification of surgical margins, with any areas of concern tagged with suture material, inked in a different colour, or submitted separately for specific histologic assessment. Surgical margins and tumour grade are important in determining the need and type of further treatment. For instance, tumour grade is important in deciding whether a soft tissue sarcoma resected with clean but close surgical margins (i.e., 1 to 3 mm) will require further local treatment because these margins may be adequate with a low-grade soft tissue sarcoma but not with a high-grade soft tissue sarcoma. Historically, the management of incompletely excised soft issue sarcomas, comprised either a second aggressive surgery or RT because the entire surgical wound was considered contaminated and neoplastic. However, recent evidence suggests that this may not necessarily be true and a more conservative approach may be employed, particularly for low-grade soft tissue sarcomas: In one study, histologic evidence of residual tumour was identified in only 22% of 39 dogs with incompletely excised tumours and, following excision of the surgical scar in these dogs with 0.5- to 3.5-cm margins, the Staffordshire & Derbyshire Clinical Club 9 th May 2018 4

local recurrence rate was 15%, with a median follow-up of 816 days. Residual tumour was not useful in predicting local recurrence. In a study of 104 canine soft tissue sarcomas managed with surgery alone in non-referral practices, fewer than 10% were excised with 3-cm margins and local tumour recurrence was reported in 28% of dogs. In a study of 139 tumours, 75% of 139 canine subcutaneous soft tissue sarcomas were incompletely excised and the local recurrence rate was 7% (grade I), 34% (grade II) and 75% (grade III). In a study of 35 dogs with low-grade soft tissue sarcomas of the extremities (below the elbow and stifle), 11% of 35 dogs had local tumour recurrence following marginal excision, and the median DFI and survival time were not reached after 1000 days. In a study of 26 dogs with incompletely excised soft tissue sarcomas of the distal limb, local recurrence was seen in 37% and only 12% of dogs were euthanised due to local disease. 40% of the dogs with local recurrence were not treated and all died of tumour-related disease, whereas 60% had further conservative surgery, and only 1/3 died from tumour-related disease. Factors that were associated with an increased risk of local recurrence in these studies were: Tumour morphology: Infiltrative vs well-circumscribed Histological grade: Grade II vs grade I/II Margins of excision: Incomplete vs complete The local recurrence rate following re-excision of an incompletely excised sarcoma is 15%, which compares favourably to a local recurrence rate of 17 to 37% for irradiation of an incompletely excised sarcoma. While these are not treatments applied to comparable groups of animals, a repeat excision, even with narrower margins than might be applied for definitive excision, is a reasonable therapy. The choice may depend on whether gross tumour tissue is left behind, the initial intent of the first surgery (e.g. curative intent vs shelling out ) and the location of the tumour. Based on the evidence above, dogs with incompletely excised soft tissue sarcomas, especially grade I and perhaps grade II tumours, can be managed with either active surveillance or a staging surgery. Active surveillance comprises monitoring of the surgical site (i.e. frequent observation for local tumour recurrence and appropriate treatment if the tumour recurs) every month for 3 months, then every 3 months for a year, then every 6 months thereafter. Staging surgery is a decision-making surgery in which the surgical scar is excised with minimal margins (0.5 to 1.0 cm) to determine if there is histological evidence of residual tumour cells. If there is no evidence of tumour cells, then no further treatment is required and these dogs should be monitored regularly as above for local tumour recurrence. Up to 40% of tumours may have no evidence of neoplastic cells in the tissue submitted after staging excision If there is evidence of residual tumour cells on staging resection, the options are: Wide resection of the surgical scar with the same margins recommended for primary soft tissue sarcomas (3 cm lateral to the tumour and one fascial layer deep to the tumour) Irradiation of the entire surgical scar Metronomic chemotherapy In humans, surgery provides better local control than adjunctive RT. Metronomic (i.e. continuous, low-dose continuous) chemotherapy comprises a COX-2 inhibitor and low-dose cyclophosphamide. In 30 dogs with incompletely excised soft tissue sarcomas this therapy resulted in a significantly prolonged DFI (410 days) when compared to a non-randomised historical control group (211 days) of 85 dogs. However, additional studies are needed to confirm this treatment alternative. Surgery and Radiation Therapy RT can be used as an adjunct to surgery following either planned marginal resection or unplanned incomplete resection. Marginal surgical resection followed by full-course postoperative RT is an attractive alternative to limb amputation for extremity soft tissue sarcoma, to preserve limb function, but this multimodality approach requires additional planning and expense. The cytoreductive surgery involves complete removal of all grossly visible tumour and then marking the lateral, proximal, and distal extents of the surgical field with radiopaque clips to assist in planning of RT. RT should be started a minimum of 7 days postoperatively to minimise the risk of radiation-induced wound healing complications such as delayed healing and dehiscence. Full-course fractionated protocols are recommended with reported schedules including 3.0 to 4.2 Gy fractions on a Monday-to-Friday or Monday-Wednesday-Friday schedule for a total dose of 42 to 63 Gy. The optimal fractionation and total dose schemes for canine soft tissue Staffordshire & Derbyshire Clinical Club 9 th May 2018 5

sarcoma have not been determined, local tumour control is better with higher cumulative doses and cumulative doses greater than 50 Gy are recommended. Acute side effects of RT such as moist desquamation are relatively mild and transient. Local tumour control and survival time are excellent when incompletely resected soft tissue sarcomas are treated with postoperative RT. The median time to local recurrence is 700 days to more than 798 days, with local tumour recurrence reported in 5% to 30% of dogs by 1 year and 16% to 60% of dogs in the long term. The overall MST for incompletely resected non-oral soft tissue sarcomas treated with postoperative RT is 2270 days with 2-, 4-, and 5- year survival rates of 87%, 81%, and 76%, respectively. Radiation Therapy RT can be employed along with surgery in the treatment of soft tissue sarcomas with a curative intent, either preoperatively or postoperatively, or as a sole treatment. Radiotherapy alone, as a single modality at a total dose of 50 Gy, results in tumour control rates of 50% at 1 year and 33% at 2 years. Measurable and palpable (i.e. macroscopic) soft tissue sarcomas are resistant to long-term control with conventional doses of irradiation alone (40 to 48 Gy). Although a complete response may be seen in up to 30% of tumours with RT alone, tumours do not regress rapidly after radiation, and the response is not generally durable. As a single modality, RT is generally considered palliative with control defined as a slowly regressing or stable disease. Higher doses of irradiation will have higher control rates, but the chances of normal tissue complications will also increase. Palliative radiation with 4 fractions of 8 Gy for a total dose of 32 Gy, has similar results to full-course radiation with a 50% response rate, median time to progression of 155 days, and a MST of 309 days. A palliative radiotherapy protocol (three 8 Gy fractions on days 0, 7, 21, or weekly) results in stable disease in 87% of dogs with a median time to progression and median survival time of 263 and 332 days with a low likelihood of serious complications. Radiation combined with hyperthermia may result in improved local control and may also decrease the time to recurrence. The median duration of local control with RT plus hyperthermia is 750 days, which is significantly greater than the 350 days with RT alone. However, the difficulty in homogeneous heating of large tumours limits this regime, and addition of whole-body hyperthermia does not improve the response rate and may increase the risk for metastasis. The combination of radiation (either post-operatively or pre-operatively) and surgery provides good long-term local control. Postoperative irradiation may be utilized if surgical removal is incomplete and further surgery is not feasible. Irradiation of microscopic tumours after excision is generally superior to radiation of measurable tumours. Control rates for adjuvant radiation after histologically incomplete resection of soft tissue sarcomas are 80% to 95% at 1 year and 72% to 91% at 2 years, with an expected 3-year and 5-year survival rate of 68% to 76%, respectively. Dogs with soft tissue sarcomas with a mitotic rate greater than 9/10 HPF are more likely to have local tumour recurrence and shorter survival times. Preoperative RT is becoming more commonly used in veterinary oncology. The rationale and advantages of administering RT prior to surgery are that (1) the radiation field is smaller because, after surgery, the entire surgical site must be included in the field and this may contribute to local toxicity; (2) a large number of peripheral tumour cells are inactivated (with reduced contamination of the surgical site); and (3) tumour reduction may make surgical resection less difficult. However pre-operative radiotherapy may increase the risk of wound healing complications, and this leads to a lower RT dose. Preoperative radiotherapy is reserved for initially inoperable tumours as an alternative to radical surgery. Chemotherapy The role of chemotherapy in the management of dogs with soft tissue sarcoma is not clear, probably because of the heterogeneity of the group. The metastatic rate for cutaneous soft tissue sarcoma is grade dependent and varies from less than 15% for grade I and II soft tissue sarcoma to 41% for grade III soft tissue sarcoma. Metastasis often occurs late in the disease, with a median time to metastasis of 365 days, and this may minimise the beneficial effects of postoperative chemotherapy on the development of metastatic disease. However, postoperative chemotherapy should be considered for: dogs with grade III soft tissue sarcoma; metastatic disease; intra-abdominal soft tissue sarcoma (e.g. leiomyosarcoma and splenic sarcoma); histologic subtypes with a higher rate of metastasis, such as histiocytic sarcomas, hypodermal HSA (stage II or III), synovial cell sarcoma, rhabdomyosarcoma, and lymphangiosarcoma; and possibly tumours not amenable to treatment with surgery or radiotherapy. Doxorubicin-based protocols, either alone or in combination with cyclophosphamide and/or vincristine, have shown the most promise in dogs with soft tissue sarcoma with an overall response rate of 23%. Single-agent doxorubicin is as equally in the management of dogs with HSAs as doxorubicin combined with either cyclophosphamide or cyclophosphamide and vincristine. Mitoxantrone, has a variable effect against soft tissue sarcomas in dogs, with the response rate varying from 0% to 33%, and ifosfamide has a complete response rate of 15%. In humans, doxorubicin and ifosfamide are the most effective single agents in the management of soft tissue sarcoma, but response rates are less than 30% and single-agent and multiple-agent chemotherapy protocols do not significantly increase overall survival times compared to surgery alone. Similarly, dogs with grade III soft tissue Staffordshire & Derbyshire Clinical Club 9 th May 2018 6

sarcomas treated with surgery and adjuvant doxorubicin show no improvement in overall survival compared to surgery alone. In humans, postoperative chemotherapy improves disease-free survival time, but not overall survival time, regardless of histologic grade. Adjuvant systemic chemotherapy has not shown the same effect on local tumour control in dogs with soft tissue sarcomas, but metronomic and local chemotherapy protocols may be effective in reducing the rate of local tumour recurrence and improving DFI in dogs with soft tissue sarcomas. Metronomic chemotherapy has been shown to prolong DFI in a small group of dogs with incompletely excised soft tissue sarcomas. Local release of cisplatin from a biodegradable polymer implanted into the surgical bed of incompletely resected soft tissue sarcomas may also decrease local recurrence, albeit with a greater risk of wound healing complications. Prognosis The overall prognosis for most dogs with soft tissue sarcoma is good, with local recurrence being the main concern for most animals and metastasis being a concern for a smaller number. Prognosis: local recurrence Local tumour control is the most challenging aspect of managing soft tissue sarcomas, and local tumour recurrence rates following either surgery alone or surgery and RT varies from 7% to 32%. Poor prognostic factors for local tumour control include large tumour size, incomplete surgical margins, and high histologic tumour grade. The rate of local recurrence is increased 11 fold for tumours with incomplete excision compared to those with complete margins of excision. Tumour size has a negative effect on local tumour control, but this is probably because of the difficulty in achieving a complete excision in a given locations, rather than size per se. Tumour size does not influence local tumour control in dogs treated with surgery and adjuvant RT or RT alone. Tumour recurrence following incomplete excision is grade dependent, with rates of 7% for grade I tumours, 34% for grade II tumours, and 75% for grade III tumours. Management of recurrent soft tissue sarcomas is more difficult than management of primary tumours, which emphasizes the need for an aggressive approach initially. Curative-intent treatment of recurrent soft tissue sarcomas often requires a more aggressive approach, resulting in increased treatment-related morbidity, shorter DFI and MST, and a higher metastatic rate compared to naïve tumours. Local tumour recurrence is still possible after either histologically complete excision or incomplete excision and adjuvant RT. Consequently, examination of the treatment site is recommended at regular intervals, such as monthly for the first 3 months, then every 3 months for the first 12 months, and then every 6 months thereafter. In one report of 75 dogs, the median time to local tumour recurrence was 368 days which emphasizes the need for long-term follow-up in these cases. Surgical excision and radiotherapy provides good local control, with a median time to local recurrence of 700 days to >798 days. Local recurrence is reported in 5-30% at 1 year and 16-60% in the long-term. Prognosis: Metastasis The overall metastatic rate in dogs with soft tissue sarcoma varies from 8% to 17% with a median time to metastasis of 365 days. Factors that increase the risk of metastatic disease include histological grade, number of mitotic figures, percentage of tumour necrosis, and local tumour recurrence. The metastatic rate for dogs with grade I or II soft tissue sarcomas is less than 15% compared to 41% to 44% for grade III soft tissue sarcomas. Metastasis is 5 times more likely when tumours have a mitotic rate of 20 or more mitotic figures/10 HPF compared to fewer than 20 mitotic figures/10 HPF. Prognosis: Overall survival The MST for dogs with soft tissue sarcoma treated with surgery alone is 1416 days with a 1year survival rate of 90-93%. The MST for surgery and adjuvant radiotherapy is 2270 days, with survival rates of 87% at 2 years, 81% at 3 years and 76% at 5 years. Following radiotherapy alone, the survival rates are 50% at 1 year and 33% at 2 years. Overall, only 10 to 33% of dogs eventually die of tumour-related causes. Tumour-related death in dogs with soft tissue sarcoma is 2.8 times more likely with greater than 10% tumour necrosis and 2.6 times more likely with a mitotic rate of 20 or more mitotic figures/10 HPF. The MSTs for dogs according to mitotic index is 1444 days with 10 or fewer mitotic figures/10hpf, 532 days with10 to 19/10hpf, and 236 days with 20 or more /10 HPF. Animals with a tumour whose proliferation index is greater than the median have an increased likelihood of dying from tumour-related causes, estimate to be 11.3 times more likely for AgNOR and 12.2 times more likely for Ki-67. The median survival of dogs with incompletely excised tumours is 657 days, compared to >1306 days for completely excised tumours. The prognosis for specific subtypes of soft tissue sarcoma is discussed below. Staffordshire & Derbyshire Clinical Club 9 th May 2018 7

Specific Tumour Types Soft tissue sarcoma is a general term for a number of different types of tumours with similar histological features and biological behaviour. The histogenesis of soft tissue sarcomas is controversial and may be difficult to differentiate on the basis of routine histologic and immunohistochemical analysis. Some pathologists have recommended the use of a more generic term such as soft tissue sarcoma or spindle cell tumour of canine soft tissue because of the difficulty in differentiating tumours such as fibrosarcoma, PNST, and haemangiopericytoma. Importantly, histological designation of tumour type is of limited relevance because most soft tissue sarcomas have a similar biologic behaviour (i.e. local invasion with a low-to-moderate metastatic rate). Atypical soft tissue sarcomas and non-soft tissue sarcomas differ in this respect. Tumours of Fibrous Origin Nodular Fasciitis (Fibromatosis, Pseudosarcomatous Fibromatosis) Nodular fasciitis is a benign non-neoplastic lesion arising in the subcutaneous fascia or superficial portions of the deep fascia in dogs. Lesions are usually nodular, poorly circumscribed, and very invasive. Histologically, large plump or spindle-shaped fibroblasts in a stromal network of variable amounts of collagen and reticular fibres with scattered lymphocytes, plasma cells, and macrophages are seen. Infantile desmoid-type fibromatosis is a histological variant characterised by fibroblast proliferation with a dense reticular fibre network and mucoid material. Theism condition may be misdiagnosed as fibrosarcoma. Wide excision of these lesions is usually curative. Local recurrence is possible with incomplete resection, but these tumours do not metastasize. Fibrosarcoma Fibrosarcomas are tumours of fibroblasts and most arise from the skin, subcutaneous tissue, or oral cavity. Tumours can be well differentiated, comprising spindle-shaped tumour cells and scant cytoplasm, or anaplastic comprising a more cellular lesion with closely packed spindle-shaped fibroblasts showing a high mitotic rate and marked cellular pleomorphism. Tumours tend to occur in older dogs and cats with no general breed or sex predilection, apart from a possible predilection for golden retrievers and Dobermanns. These tumours are infiltrative, with microscopic tumour cells invading along fascial planes, and often recur after surgical excision. Metastasis is uncommon, but may be seen in the lungs, liver, bone brain and skin. Tumours arising from the oral cavity generally behave in a more malignant fashion and have a poorer prognosis due to this behaviour and the increased difficulty in obtaining local control. A unique form, histologically low-grade, yet biologically high-grade fibrosarcoma, may occur in the oral cavity. Despite an apparent bland appearance on histological examination, this form has a tendency to grow to a large size, invade deeper structures, including bone, and metastasise in up to 20% of the cases. Tumours of the Peripheral Nerves Peripheral Nerve Sheath Tumour (Neurofibrosarcoma, Malignant Schwannoma, Haemangiopericytoma) The PNSTs are malignant tumours of nerve sheath origin and have also been referred to as neurofibrosarcoma, malignant schwannoma, and haemangiopericytoma. Most haemangiopericytomas will have features of nerve sheath tumours histologically, and origin from blood vessel pericyte has yet to be proven. Malignant PNSTs will label positively with S-100 and vimentin, indicating peripheral nerve origin. The reported incidence is 0.5% 2% of all skin tumours in dogs, although these results vary considerably between studies, depending on the classification of these tumours. They are locally aggressive but metastasis is uncommon (<20% in dogs). These tumours can occur anywhere in the body, and may be divided anatomically, which has some relevance for surgical management: Peripheral group: involve nerves away from the brain or spinal cord Plexus group: involve nerves of the brachial or lumbosacral plexus Root group: involve nerves immediately adjacent to the brain or spinal cord Despite appearing encapsulated at surgery, these tumours are similar to fibrosarcomas and histologically they are poorly defined tumours without histological encapsulation. Most tumours are adherent to deeper tissues and may infiltrate surrounding fascia, muscle, and skin. Although these are malignant tumours, they have a low metastatic rate, but local recurrence is common after conservative surgery. They tend to grow slowly and can reach a large size. They can easily be confused with lipomas on initial clinical examination, which, in the absence of a biopsy, may lead to an inappropriate local excision. Plexus or root PNSTs may result in the compression of nerves. Most patients will show signs of unilateral lameness, muscle atrophy, paralysis, and pain. They can invade the spinal cord, and about 50% of grade III tumours will do so. Local disease usually limits survival before metastasis occurs. Histiocytic Disorders The biology, nomenclature, and management of this collection of benign and malignant conditions is confusing and continues to develop, and this tumour type will not be dealt with in detail here. The entity of malignant fibrous histiocytoma may be more consistent with soft tissue sarcomas in general and is managed in a similar manner. Staffordshire & Derbyshire Clinical Club 9 th May 2018 8

Tumours of Adipose Tissue Tumours arising from adipose tissue may be classified as lipoma, intermuscular lipoma, invasive or infiltrative lipoma and liposarcoma. Lipoma Lipomas are benign tumours of adipose tissue, although variants such as angiolipoma and angiofibrolipoma have been described. Lipomas are relatively common in older dogs, especially in subcutaneous locations, and are rarely symptomatic. Lipomas can also occur in the thoracic cavity, abdominal cavity, pelvis, spinal canal, and vulva and vagina of dogs and can cause clinical signs due compression (e.g. pericardial lipoma) or strangulation of adjacent tissue (e.g. intestine). Parosteal and infiltrative lipomas are rarely reported but they may have a more aggressive behaviour despite their benign histologic appearance. Superficial tumours usually appear as soft, well-circumscribed, smooth, subcutaneous singular masses on the trunk or proximal extremities. Marginal resection is recommended for lipomas that interfere with normal function. Surgical resection is usually curative, but local recurrence has been reported. Multiple lesions represent multiple primary tumours, not metastasis. Intermuscular Lipoma Intermuscular lipomas are a variant of the subcutaneous lipoma located between muscles, often in the caudal and medial thigh of dogs. Clinically, intermuscular lipomas appear as a slow-growing, firm, and fixed mass in the caudal and medial thigh region and may occasionally cause lameness. Cytological analysis of fine-needle aspirates is usually diagnostic and radiographs or CT show a uniform fat opacity. The recommended treatment is surgical resection, usually with blunt dissection. The prognosis is excellent with recurrence being very uncommon after surgical removal. Infiltrative (Invasive) Lipoma Infiltrative lipomas are uncommon tumours composed of well-differentiated adipose cells without evidence of anaplasia. Differentiation from lipoma may not be possible with cytology or small biopsy specimens. While they are considered benign and do not metastasise, they are locally aggressive and may invade adjacent muscle, fascia, nerve, myocardium, joint capsule, and even bone. Clinically, they may be painful, are less well-defined than lipomas and palpate as a firm or solid mass because of their infiltrative behaviour. Definitive diagnosis can only be made by the histologic evaluation of surgically excised tissue at the edge of the tumour and adjacent normal tissue. CT is useful to delineate these tumours, particularly at the margins of the tumour where there is invasion into surrounding tissue, especially muscle, but differentiation of infiltrative lipomas from normal fat is problematic, which can predispose to incomplete excision and local recurrence in up to 36% of dogs. A female predisposition to this tumour type has been reported. Local excision may be followed by recurrence and a wide local or radical local excision, as for other soft tissue sarcomas, may be needed for local control. Aggressive treatment, including amputation, may be necessary for local control. RT can be considered either alone or in combination with surgical excision. Surgical liposuction of the mass of the tumour leads to DFIs of approximately 1 year. Liposarcoma Liposarcomas are uncommon malignant tumours originating from lipoblasts. There is no evidence that they arise from malignant transformation of lipomas. They are usually reported in subcutaneous locations, especially along the ventrum and extremities, but can also occur in other primary sites such as bone and the abdominal cavity. They are locally invasive with a low metastatic potential to the lungs, liver, spleen, and bone. Liposarcomas can be differentiated from lipomas based on the clinical features, imaging findings, and histological appearance. Liposarcomas tend to be firm, poorly circumscribed with a more rapid rate of growth, and on radiographs or CT, they may lack a uniform, homogenous fat opacity, and may have varying components of soft tissue within them. Histologically, liposarcomas are characterized by increased cellularity, distinct nuclei, and abundant cytoplasm with one or more droplets of fat. The prognosis for liposarcoma is good with appropriate surgical management. The median survival time (MST) following wide surgical excision is 1,188 days, which is significantly better than either marginal excision (649 days) or incisional biopsy (183 days). Liposarcoma is histologically classified as well-differentiated, myxoid, round cell (or poorly differentiated), pleomorphic, or dedifferentiated. This classification scheme has clinical and prognostic importance in humans because pleomorphic liposarcomas have a high metastatic rate, myxoid liposarcomas are more likely to metastasize to extrapulmonary soft tissue structures, and well-differentiated liposarcomas are unlikely to metastasize, but in dogs, histologic subtype has not been found to be prognostic, although metastatic disease is more common with pleomorphic liposarcomas. Tumour size and location is not reported to have prognostic significance. Staffordshire & Derbyshire Clinical Club 9 th May 2018 9

Tumours of Smooth Muscle Leiomyoma and Leiomyosarcoma Leiomyomas and leiomyosarcomas are tumours arising from smooth muscle cells. The gastrointestinal (GI) tract is most commonly affected, but other primary sites include the spleen, liver, urogenital tract, retroperitoneal space, vessel wall, and subcutaneous tissue. Cutaneous smooth muscle is present in three separate locations: arrector pili muscles, blood vessel walls, and genital/areolar skin and benign or malignant smooth muscle tumours may arise from each of these locations. Leiomyosarcomas of the skin do not tend to metastasize, in contrast to visceral leiomyosarcomas, and surgical removal of the lesions is the treatment of choice. Paraneoplastic syndromes associated with smooth muscle tumours, particularly GI leiomyomas and leiomyosarcomas, include hypoglycaemia, nephrogenic diabetes insipidus, and secondary erythrocytosis. Leiomyomas are benign and usually small, localised, and well encapsulated. Leiomyomas of the vagina and vulva are often pedunculated and may protrude from the vulva. These tumours are hormonally dependent and ovariohysterectomy is recommended. GI leiomyomas tend to be found in the stomach, rather than the jejunum and caecum. Leiomyosarcomas are malignant tumours with a moderate metastatic potential, depending on the primary site, being up to 100% for hepatic leiomyosarcoma, approximately 50% for other primary intra-abdominal sites and 0% for dermal smooth muscle tumours. The most common sites for metastasis of GI tumours are regional lymph nodes, mesentery and liver although other sites include the spleen, kidneys, and peritoneum. Leiomyosarcoma is the second most common GI tumour in dogs and has a predilection for the jejunum and caecum, although they may arise from the oesophagus to the rectum. An immunohistochemical review of previously diagnosed GI leiomyomas and leiomyosarcomas has resulted in many of these tumours being reclassified as GI stromal tumours (GISTs) or GI stromal-like tumours. Leiomyosarcomas have strong immunoreactivity to actin and desmin and rarely label positively with c-kit, CD34, or S-100 protein. GISTs are consistently associated tyrosine kinase receptor gene c-kit mutations and have strong immunoreactivity to c-kit and CD34 proteins with variable labelling for to actin, desmin and S-100 protein. The GI stromal-like tumours have similar profile to GISTs, but they do not express c-kit. The tumours are more common in older dogs, with no distinct breed or sex predilection, apart from male dogs being more commonly affected by GI leiomyomas. Presenting signs can include inappetence, weight loss, vomiting, diarrhoea, polyuria, polydipsia, anaemia, and hypoglycaemia. Intestinal perforation with localized to diffuse peritonitis may occur in up to 50% of dogs with GI leiomyosarcoma. Surgical resection is the recommended treatment for dogs with leiomyosarcomas. Local tumour control is good following complete resection, but recurrence has been reported following incomplete resection of a gastric leiomyoma and cutaneous leiomyosarcomas. Prolonged survival and possibly cure has been reported following surgery in dogs with gastrointestinal leiomyosarcoma and GISTs. Prognostic factors in humans with GIST include tumour size, metastasis, and histologic criteria such as tumour necrosis, number of mitotic figures, and proliferating cell nuclear antigen (PCNA) index, but prognostic factors have not been investigated in dogs with leiomyosarcoma. The MST for dogs with GI leiomyosarcoma and GIST surviving the immediate postoperative period is up to 37.4 months, with 1-, 2-, and 3-year survival rates of 75% to 83%, 62% to 67%, and 60%, respectively. The influence of metastatic disease on survival is controversial, with evidence that it may affect survival, but also evidence that survival may be prolonged (MST 21.7 months). The MST for dogs with splenic leiomyosarcoma is 8 months, and in one series, all dogs with hepatic leiomyosarcoma had evidence of metastasis at initial surgery and were euthanised. Tumours of Skeletal Muscle Rhabdomyosarcoma Rhabdomyosarcomas are rare malignant tumours originating from myoblasts or primitive mesenchymal cells capable of differentiating into striated muscle cells. In dogs, rhabdomyosarcomas are most frequently reported to arise from skeletal muscle of the tongue, larynx, myocardium, and urinary bladder. They are locally invasive with a low-to-moderate metastatic potential to the lungs, liver, spleen, kidneys, and adrenal glands. Rhabdomyosarcomas may be histologically classified as embryonal, botryoid, alveolar, and pleomorphic, and this scheme has prognostic significance in humans, but it has not been investigated in dogs. In humans, botryoid rhabdomyosarcoma has a good prognosis, embryonal rhabdomyosarcoma has an intermediate prognosis, and alveolar rhabdomyosarcoma has a poor prognosis. A histologic diagnosis of rhabdomyosarcoma may be difficult and immunohistochemical labelling for vimentin, skeletal muscle actin, myoglobin, myogenin, and myogenic differentiation (MyoD) may be required for a definitive diagnosis and to rule out haemangiosarcoma and histiocytic sarcoma. Embryonal rhabdomyosarcomas have a predilection for the head and neck region of older dogs, such as the tongue, oral cavity, and larynx. In contrast, Staffordshire & Derbyshire Clinical Club 9 th May 2018 10

botryoid rhabdomyosarcoma commonly arises in the urinary bladder of young, large breed dogs with a possible predilection for female dogs and the Saint Bernard breed. Botryoid tumours are characterized by their grapelike appearance. Rhabdomyosarcomas, particularly those involving the extremities, have a high rate of metastasis in humans, mainly to the lungs, lymph nodes, and bone marrow. The metastatic potential and prognosis in dogs with rhabdomyosarcoma is not clear as it is not commonly diagnosed and even less commonly treated. The metastatic rate for orbital rhabdomyosarcoma is higher for young dogs less than 4 years old (56%) compared to older dogs (0%). In the few dogs treated with surgical resection with or without RT and chemotherapy, disease-free and overall survival times in non-juvenile dogs have been encouraging. In humans, multimodality treatment with surgery, RT, and chemotherapy has significantly improved survival rates, particularly in children with embryonal and botryoid rhabdomyosarcoma. Tumours of Vascular and Lymphatic Tissue Lymphangiosarcoma Lymphangiosarcomas are rare tumours, usually seen in medium to large breed dogs more than 5 years old, that arise from lymphatic endothelial cells. They are usually soft, cystic-like, and oedematous, masses in the subcutaneous tissues and clinical signs are often associated with extensive oedema and leakage of lymph through the skin or a cystic mass. A fine needle aspirate may reveal a fluid-filled mass. Histopathologically, these tumours resemble normal endothelial cells with vascular channels, and should be differentiated from haemangiosarcoma, mainly on the lack of red blood cells in the vascular spaces. Lymphangiosarcomas tend to have a moderate-to-high metastatic potential. There is some evidence of efficacy of adjuvant doxorubicin therapy after surgery. Haemangioma Haemangiomas and haemangiosarcoma (HSA) are tumours of vascular endothelial origin. Haemangioma is a benign tumour that can occur in a number of locations, including skin, liver, spleen, kidneys, bone, tongue, and heart. Dermal haemangiomas may be induced by ultraviolet (UV) light in short-haired dogs with poorly pigmented skin. Although their biological behaviour is benign, they may cause anaemia secondary to tumour-associated blood loss. In humans, haemangiomas can spontaneously regress or be responsive to intralesional corticosteroids, but this has not been observed in dogs. Complete surgical excision is usually curative. Haemangiosarcoma HSA is a highly malignant tumour arising from vascular endothelial cells. HSA accounts for less than 1% of all skin tumours in dogs and 17% 35% of all HSA, are cutaneous. It commonly arises from the viscera, especially the spleen, right atrial appendage, and liver, but may also develop from the skin, pericardium, lung, kidneys, oral cavity, muscle, bone, urogenital tract, peritoneum and retroperitoneum. Only dermal and subcutaneous HSA will be considered here. Primary dermal HSA has a predilection for light haired or poorly pigmented skin on the ventral abdomen, medial thigh and inguinal region, and UV radiation has been proposed as a predisposing cause. Skin HSA vary in size, are poorly circumscribed, dark and soft, and may resemble bruises or ecchymoses. Alopoecia, ulceration, and haemorrhage are common, and animals may present with a haematoma. Canine cutaneous HSAs are staged according to tumour depth and invasion: superficial tumours, confined to the dermis (stage I), tumours extending into subcutaneous tissues (stage II), and tumours invading muscle and fascia (stage III). Stage II and III dermal HSA are typically large and poorly circumscribed with have a bruised appearance that may be mistaken for a haematoma. Treatment is wide surgical excision and adjuvant chemotherapy. Tumour-free surgical margins are more likely to be achieved in cutaneous than subcutaneous lesions and are therefore associated with longer survival times. Completeness of excision is the most important prognostic factor with disease-free intervals (DFIs) of at least 1 year for completely excised skin HSAs. Similarly, dermal location is associated with more complete resections compared to a subcutaneous location. Subcutaneous HSA (stage II) are more biologically aggressive than the cutaneous (stage I) form and are more likely to recur locally and result in euthanasia or death. Younger age (<9 years) is associated with longer DFI and survival times in dogs with subcutaneous tumours. Clinical staging provides prognostic information on the success of local treatment, metastatic potential, and survival time. Dogs with stage I dermal HSAs have a complete surgical resection rate of 78%, a 30% metastatic rate (all to distant dermal sites) and a MST of 780 days. In contrast, dogs with stage II and III hypodermal HSAs have a complete surgical resection rate of only 23%, because the tumours are larger and less well circumscribed, a 60% metastatic rate (lungs, regional lymph nodes, and distant dermal sites) and a significantly lower MST of 172 (stage II) to 307 (stage III) days. Chemotherapy may be a viable adjunctive therapy, especially for incompletely resected tumours. The median survival time for dogs with cutaneous HSA treated with surgery and chemotherapy is reported as 211 days (doxorubicin, and cyclophosphamide), 425 days (vincristine, doxorubicin, and cyclophosphamide) and 1,189 days (doxorubicin). Staffordshire & Derbyshire Clinical Club 9 th May 2018 11