Malignant Fibrous Histiocytoma Involving the Ilium in a Cat

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1 Brief Communication 513 Tumour Pathology, Sec. Series, Fasc. 8. Armed Forces Institute of Pathology, Washington, NIEBERLE, K.; COHRS, P.: Lehrbuch der speziellen pathologischen Anatomie der Haustiere, pp , 5. Aufl. Fischer, Stuttgart, NIELSEN, S.W.; MISDORP, W.; MCENTEE, K.: Tumours of the ovary. In: International histological classification of tumours of domestic animals. Bull WHO , NIELSEN, S.W.: Personal Communication, NORRIS, H.J.; GARNER, F.M.; TAYLOR, H.B.: Pathology of feline ovarian neoplasms. J Path , PICK, L.: Uber Neubildungen am Genitale bei Zwittern nebst Beitragen zur Lehre von den Adenomen des Hodens und Eierstockes. Arch Gynaekol , PUGH, R.C.B.: Pathology of the testis, pp Blackwell Scientific Publications, Oxford, London, Edinburgh, Melbourne, SBERNARDORI, U.; NAVA, A.: Disgerminoma dell'ovaio nella gatta. Clin Vet (Milano) 91: , SCULLY, R.E.: Sex cord-stromal tumors. In: Pathology of the female genital tract, ed. Blaustein, pp Springer, New York, Heidelberg, Berlin, SEROV, S.F.; SCULLY, R.E.; SOBIN, L.H.: Histological typing of ovarian turnours, pp World Health Organization, Geneva, TEILUM, G.: Classification of testicular and ovarian androblastoma and Sertoli cell tumours. Cancer 11: , TEILUM, G.: Special tumours of ovary and testis, pp Munksgaard, Copenhagen, 1971 Request reprints from Prof. Dr. W. Hofmann, Institute of Pathology, University of Heidelberg, Im Neuenheimer Feld 220/221, Postfach , D-6900 Heidelberg 1 (West Germany) Malignant Fibrous Histiocytoma Involving the Ilium in a Cat R. J. SEILER and G. T. WILKINSON In recent years there has been extensive recognition and documentation of a heterogenous group of human neoplasms characterized morphologically by cells with histiocytic and fibroblastic qualities [5, 8, 10, 18, 19, 21,231. There are now convincing data from tissue culture and ultrastructural studies to suggest a common histogenesis of these cells [8, 191. The generic term fibrous histiocytoma is used for those varieties considered benign. The less common malignant group includes the atypical fibrous histiocytoma, malignant fibrous histiocytoma, malignant histiocytoma and epithelioid sarcoma [8, 15, Malignant fibrous histiocytoma was diagnosed recently in three cats and two dogs [9], and there are a few earlier reports of morphologically similar tumors in the dog, cat and horse [ 1, 7, 12, 16, 171. A 2-year-oId, neutered female, domestic short hair cat was referred to the University of Queensland Veterinary Clinic with a rapidly growing, firm mass over the left ilium. Within 6 weeks the tumor had increased in size to about 10 X 7 cm. The cat was depressed, dehydrated

2 514 Seiler and Wilkinson Fig. 1: Radiograph. Lysis of left ilium and soft tissue swelling. Fig. 2 Typical accumulation of giant cells. HE. Fig. 3 Sheets of histiocytic cells in stroma. HE. Fig. 4 Low power view of more fibroblastic area of stroma. Arrangement of short fascicles of cells and their processes suggests storiform pattern. HE.

3 Malignant Fibrous Histiocytoma 515 and emaciated. It had pale mucous membranes and a rough staring coat. The left leg was dragged in extension with knuckling over of the left hind paw and atrophy of muscles of the left thigh. Pain perception was present but there was no withdrawal reflex in the affected limb. Radiography showed extensive lysis of the ilium and marked soft tissue swelling over the area (fig. I). The prognosis was poor and the cat was killed and necropsied. Samples for histological examination were taken from various sites in the tumor, adjacent lymph nodes and all other major organs, and fmed in 10% formalin. Frozen and paraffin-embedded sections were prepared; only those samples containing remnants of the ilium required decalcification. Sections were stained routinely with haematoxylin and eosin (HE), periodic acid-schiff (PAS) with and without amylase pretreatment, Masson s trichrome, Perk Prussian blue, Gomori s reticulin stain, phosphotungstic acid haematoxylin (PTAH), toluidine blue and oil red 0. The large multinodular tumor occupied much of the left ilium anterior to the acetabulum and bulged outward, displacing and infiltrating the overlying tissues. The sciatic nerve was compressed and slightly displaced, and neoplastic tissue penetrated slightly into the sacrolumbar intervertebral foramen. Cut surfaces were pale grey to white and fleshy. Small pink or white necrotic flecks were scattered through most sections and occasional gritty spicules of bone remained along the iliac border. Histologically, irregular nodules of neoplastic tissue permeated among disintegrating remnants of the ilium. Osteogenic reaction of the ilium was absent or minimal, and there was usually an abrupt junction with unreactive bone and marrow. The free margins were circumscribed with an expanding border or slight infiltration of the overlying tissues. Scanty connective tissues partially separated the neoplastic nodules and scattered, thin-walled blood vessels coursed through the tumor. Patches of necrosis, usually with little hemorrhage, were present in most blocks. There were no metastases. The outstanding feature was the presence of many multinucleated giant cells scattered or clustered among sheets of mononuclear cells (fig. 2). Variable numbers of nuclei (maximum about 50) were arranged in the peripheral cytoplasm or clumped centrally in the giant cells. The cytoplasm had a ground glass or slightly vacuolar appearance and occasionally contained some PAS-positive, amylase resistant granular material. There were some distinct, large cytoplasmic vacuoles often containing cellular debris or live mononuclear cells. Smaller tumor giant cells were present less frequently. These had less cytoplasm, and nuclear configurations ranging from a single, huge nucleus to multilobed, binucleated and other multinucleated types. The predominant stromal cells were mononuclear and resembled histiocytes. They could be found either scattered liberally among the other cell types or in broad unpatterned sheets of uniform, epithelioid cells (fig. 3). Cohesion among these cells was poor and the cell outlines were usually distinct. Nuclei were oval, pleomorphic, and moderately vesicular with central, large nucleoli. There were some macrophage-like cells with wispy, vacuolated cytoplasm, which was usually positive for fat. Patches of stroma sometimes took on a more fibroblastic appearance, with the cells, and their more abundant cytoplasmic processes, in short fascicles arranged in a storiform pattern (fig. 4). Nuclei were more elongated than in the histiocytic cells. Mitoses, often of tripolar or other atypical forms, were frequent in all areas; 232 were counted in 50 high power (~400) fields, 10 fields from each of five different cellular areas. Collagen and reticulin fibre deposition was patchy and most obvious in slightly hyalinized patches about areas of necrosis. Some broad trabeculae of metaplastic osteoid unassociated with the neoplastic cells were found in the internodular connective tissues. Moderate numbers of inflammatory cells, chiefly lymphocytes, with some plasma cells, neutrophils and a few hemosiderin-containing macrophages, were present throughout the tumor, either as a light diffuse scattering or as small dense aggregations in the internodular tissue. There was Wallerian degeneration of nerve tissue and atrophy and degeneration of muscle compressed by the tumor. Difficulties arise in differentiating such neoplasms from various other pleomorphic sarco-

4 516 Seiler and Wilkinson mas, and in deciding the appropriate classification from the spectrum of fibrohistiocytic neoplasms. Malignant fibrous histiocytoma is characterized by cells resembling histiocytes and fibrocytes, a degree of fibrogenesis, storiform pattern, multinucleated giant cells, bizarre tumor giant cells, foam cells, inflammatory cells (mostly lymphocytes), anaplasia of stromal cells and mitotic figures (normal and atypical) [ 15, 211. Marked variability, however, is allowed within and between tumors even to the absence of some of these features [ 13, 141. Pleomorphic forms of rhabdomyosarcoma, liposarcoma, chondrosarcoma, fibrosarcoma and osteosarcoma often resemble malignant fibrous histiocytoma and may cause diagnostic confusion [5, 14, 15, 20, 221. These usually have enough distinctive features, however, to allow characterization, and any giant cells present are usually of the tumor giant cell type only. Large osteoclast-like giant cells often occur in osteosarcoma, but the neoplasm in our cat contained only minimal, metaplastic osteoid. Giant cell tumor of bone as it usually is seen in man [2,3] is quite different from the neoplasm in our cat. Pleomorphic types, more common in animals [12], could be similar, but would not be expected to have the definite histiocytic character of the stroma. We were unable to determine whether the tumor in our cat had arisen in the ilium or adjacent soft tissues. Both intraosseous and extraosseous malignant fibrous histiocytomas involving bone have been seen in man [4, 6, 13, 221. The tumor in our cat is similar in many respects to the malignant giant cell sarcoma of soft parts [lo, 15, 201 which is apparently a particularly histiocytic variant of malignant fibrous histiocytoma [I 1, 211. Extensive bony involvement is not described for that variant. Future studies of similar tumors in animals, including tissue culture of explants, are necessary to validate the synonymity we have presumed with human malignant fibrous histiocytoma. References I ALEXANDER, J.W.; RIB, R.C.; DUELAND, R.: Extraskeletal giant cell tumor in a cat. Vet Med Small Anim Clin , APARISI, T; ARBORGH, B.; ERICSSON, J.L.E.: Giant cell tumor of bone: detailed fine structural analysis of different cell components. Virchows Arch [Pathol Anat] , ASHLEY, D.J.B.: Evan s Histological Appearances of Tumours, pp , 3rd ed. Churchill Livingstone, Edinburgh, DAHLIN, D.C.; UNNI, K.K.; MATSUNO, T.: Malignant (fibrous) histiocytoma of bone: fact or fancy? Cancer , EKFORS, T.O.; RANTAKOKKO, V.: An analysis of 38 malignant fibrous histiocytomas in the extremities. Acta Pathol Microbiol Scand [A] , FELDMAN, F.; NORMAN, D.: Intra- and extraosseous malignant histiocytoma (malignant fibrous xanthoma). Radiology 1M , FORD, H.G.; EMPSON, R.N.; PLOPPER, C.G.; BROWN, P.H.: Giant cell tumor of soft parts: a report of an equine and a feline case. Vet Pathol , Fu, Y.S.; GABBIANI, G; KAYE, G.I.; LATTES, R.: Malignant soft tissue tumors of probable histiocytic origin (malignant fibrous histiocytomas): general considerations and electron microscopic and tissue culture studies. Cancer , GLEISER, C.A.; RAULSTON, G.L.; JARDINE, J.H.; GRAY, K.N.: Malignant fibrous histiocytoma in dogs and cats. Vet Pathol , GUCCION, J.G.; ENZINGER, F.M.: Malignant giant cell tumor of soft parts: an analysis of 32 cases. Cancer , 1972 I1 HAJDU, S.I.; HAJDU, E.O.: Cytopathology of Sarcomas and other Nonepithelial Malignant Tumors, pp W. B. Saunders, Philadelphia, JACOBSON, S.A.: The Comparative Pathology of the Tumors of Bone, pp , , C. C. Thomas, Springfield, Illinois, JOHNSON, W.W.; COBURN, T.P.; PRATT, C.B.; SMITH, J.W.; KUMAR, A.P.M.; DAHLIN, D.C.:

5 Malignant Fibrous Histiocytoma 517 Ultrastructure of malignant histiocytoma arising in the acromion. Hum Pathol , KEMPSON, R.L.; KYRIAKOS, M.: Fibroxanthosarcoma of the soft tissues: a type of malignant fibrous histiocytoma. Cancer , MACKENZIE, D.H.: Miscellaneous soft tissue sarcomas. In: Recent Advances in Pathology, ed. Harrison and Weinbren, pp , No. 9. Churchill Livingstone, Edinburgh, MISDORP, W.; VAN DER HEUL, R.O.: Tumors of Bones and Joints. In: International Histological Classification of Tumours of Domestic Animals. Bull WHO 53: , NIELSEN, S.W.: Extraskeletal giant cell tumor in a cat. Cornell Vet , O BRIEN, J.E.; STOUT, A.P.: Malignant fibrous xanthomas. Cancer 17: , 1964 I9 OZZELLO, L.; STOUT, A.P.; MURRAY, M.R.: Cultural characteristics of malignant histiocytomas and fibrous xanthomas. Cancer 16: , SALM, R.; SISSONS, H.A.: Giant-cell tumors of soft tissues. J Pathol , I SOULE, E.H.; ENRIQUEZ, P.: Atypical fibrous histiocytoma, malignant fibrous histiocytoma, malignant histiocytoma, and epithelioid sarcoma: a comparative study of 65 tumors. Cancer , SPANIER, S.S.; ENNEKING, W.F.; ENRIQUEZ, P.: Primary malignant fibrous histiocytoma of bone. Cancer , STOUT, A.P.; LATTES, R.: Tumors of the Soft Tissues. In: Atlas of Tumor Pathology, 2nd series, pp , Armed Forces Institute of Pathology, Washington, 1967 Request reprints from Dr. R. J. Seiler, Department of Veterinary Pathology, New York State College of Veterinary Medicine, Cornell University, Ithaca, NY (USA).