Detection of Mast Cells in the Vicinity of Peritumoral Stroma of Invasive Breast Carcinoma

Transcription

1 Med. J. Cairo Univ., Vol. 80, No. 2, June: 45-51, Detection of Mast Cells in the Vicinity of Peritumoral Stroma of Invasive Breast Carcinoma ABDALLAH M. KHALIL, M.D.; ESSAM E. AYAD, M.D.; SAMAR A. EL-SHEIKH, M.D. and LUBNA O. EL FAROUK ABDEL SALAM, M.D. The Department of Pathology, Faculty of Medicine, Cairo University Abstract Breast cancer is the most common malignancy among women worldwide with increasing incidence rates. The role of the immune system during cancer development is complex. The role of mast cells in cancer progression is still a matter of debate, as their accumulation has been associated with enhanced growth and invasion in some human cancers, and on the other hand, mast cell infiltration has been associated with good prognosis in others. This work aimed at detecting the relation between the presence of mast cells in the peritumoral stroma and other clinicopathological features, in order to identify their role as a prognostic factor in cancer breast progression. To perform this study, we collected archival blocks prepared from 40 cases of modified radical mastectomy and quadrentectomy with axillary clearance specimens diagnosed as breast carcinoma (33 invasive duct NOS, five cases of lobular carcinoma and two cases of medullary carcinoma). Cases other than invasive duct carcinoma NOS (7/40) were grouped together under the category of (others) for statistical purposes. c-kit immunohistochemical staining was evaluated in the peritumoral stroma as well as in the tumor cells. Toluidine blue stain was done to delineate stromal mast cells from singly present c-kit positive tumor cells in the stroma. This study has found no statistical correlation between mast cells and other clinicopathological variables present in cancer breast cases included like age, histological type, tumor grade, tumoral necrosis, nodal status as well as c-kit expression in tumor cells. In conclusion, these findings suggest that the role of mast cells in breast cancer is still controversial and more studies on a wider scale of patients are recommended. Key Words: Breast cancer Mast cells c-kit CD (117) Toluidine blue. Introduction BREAST cancer gains its global attention for being the most frequent malignancy among women all over the world with nearly a million new cases each year. It accounts for nearly 21% of all cancers among women worldwide [1]. Correspondence to: Dr. Samar A. El-Sheikh, Lectuer of Pathology, Pathology Department, Faculty of Medicine, Cairo University In Egypt, breast cancer was ranked as the first most common malignancy among females, representing 37.5% of all women cancer cases and 0.9% in all men corresponding ones [2]. The role of the immune system during cancer development is complex involving extensinve reciprocal interactions between genetically altered cells, adaptive and innate immune cells, their soluble mediators and structural components present in the neoplastic microinvironment [3]. In malignant tumors, the stroma surrounding the malignant cells is important for the growth and spread of the malignant tumor. The local inflammatory process, previously believed to be the host response against cancer, might actually contribute to the development of malignancy; and this response has gained increased attention [4]. Mast cells have emerged as a primary candidate among the infiltrating cell population responsible for mediating tumor promotion [ 5-7].They are versatile tissue homing secretory cells which have been implicated in various cell mediated immune reactions against infections. They have also been found to participate in angiogenic and tissue repair processes after injury [8,9]. Mast cells are derived from a specific bone marrow progenitor cell; they migrate into tissues where they mature depending on the microenvironmental conditions. These cells may promote tumor development through many different ways; also, they could facilitate tumor angiogenesis through heparin-like molecules and heparin which could further permit neovascularization and metastases through its anticlotting effects [10]. Moreover, mast cells secrete histamine and growth factors, such as a platelet derived growth factor, vascular endothelial growth factor, stem cell factor and nerve growth factor. They are also rich in metalloproteases that are responsible 45

2 46 Detection of Mast Cells in the Vicinity of Peritumoral Stroma for the majority of proteolytic components necessary for tumor invasion [5]. On the other hand, mast cells could also inhibit tumor growth by secreting several cytokines and proteolytic enzymes participating in inducing apoptosis of malignant cells, such as IL-4 [11]. The dual role of mast cells in inhibiting or promoting tumor growth needs many investigations [12]. Detection of mast cells can be undergone by several staining techniques and immunohistochemical methods. The cytoplasm of mast cells contains granules (metachromatic) composed of heparin and histamine. Toluidine blue stains mast cells red-purple (metachromatic saining) in a blue background (orthochromatic staining). Mast cells are also positive for c-kit (CD 117) immunohistochemical staining [13]. Aim of the work: Presence of mast cells in the peritumoral stroma of invasive breast carcinoma, and to evaluate the relation between their presence and other clinicopathological criteria such as patient's age, tumor type, size, grade, lymph node status and tumoral necrosis. Material and Methods Patients data and tissue samples: A retrospective study on 40 cases of malignant breast lesions (33 invasive duct NOS, five cases of lobular carcinoma and two cases of medullary carcinoma. Cases (7/40) other than invasive duct carcinoma NOS were grouped together under category of (others) for statistical purpose. All cases were collected from the files of the Pathology Department, Kasr Al-Aini Hospital, Faculty of Medicine, Cairo University from Jan to October In this study, patients were eligible to be included if they were diagnosed as invasive breast carcinoma according to WHO classification (2003) [14], and undergone modified radical mastectomy or quadrentectomy with axillary clearance to provide adequate histologic sections for proper application of immunohistochemical marker c-kit and toluidine blue histochemical staining. Tumor grading was evaluated according to Nottingham combined histologic grade (Elston-Ellis modification of the Scarff Bloom Richardson grading system 1998) [15]. The clinicopathological data were all collected, including age, sex, size, grade, nodal satus, tumoral necrosis, intraductal component and the presence of tumor vascular emboli. Tissue preparation for histopathologic examination: All specimens were formalin fixed, routinely processed and embedded in paraffin. Serial sections of 4 micron thickness were prepared from each tissue block, one of them was stained by H&E for histopathological reevaluation. Immunohistochemical staining: For immunohistochemical staining by c-kit, the formalin-fixed, paraffin wax-embedded breast tissues were immunostained for c-kit, using standard methods. Rabbit polyclonal antibody was used (code no A4502; dilution 1:200; DAKO, Glostrup, Denmark). Sections were pretreated by heat-antigen retrieval in 0.01mol/L sodium citrated buffer (ph6.0) in microwave for 15min. The sections were then cooled for 5min and rinsed in tap water. After blockage of biotin and peroxidase, immunohistochemical staining was performed. The slides were left at room tempreture for 60 minutes, and then were subsequently stained by the universal immunoperoxidase polymer method, according to the protocol provided by the manufacturer. Positive reactions were visualized with diamiobenzidine, followed by counterstaining with hematoxylin. Stromal mast cells were dilineated by c- kit immunostaining with variable intensities as well as high percentage of tumor cells. c-kit immunoreactivity was classified as as positive (membranous / cytoplasmic) and negative reaction according to the classification applied by Tsutsui and his colleagues [16]. Toluidine blue histochemical staining: For further delineation of mast cells and their differentiation from the positively stained tumor cell for c-kit, tissue sections (4 micron thickness) were prepared from the formalin-fixed, paraffinembedded tissues and stained with toluidine blue. Toluidine blue positively stained mast cells were red-purple in color in a blue background. Mast cells were observed in high-power field (40 xobjective) in each tissue section. Scoring was done according to that previously applied by Dabiri et al. [17]. In which (score 0=absent mast cells and score 1=positive for mast cells). Statistical analysis: Data were statistically described in terms of frequency (number of cases) and relative frequency (percentage). Chi square test was performed to compare the different study variables between the study groups. Yates correction and Fisher exact tests were used only when the expected frequency was found to be less than five. Probability (p) value less than 0.05 was considered statistically significant. All statistical calculations were done using computer programs Microsoft Excel version 7

3 Abdallah M. Khalil, et al. 47 (Microsoft Corporaton, NY, USA) and SPSS (Statistical Package for the Social Science; SPSS Inc., Chicago, IL, USA) statistical program. Some microscopic photos were captured using digital camera attached to an Olympus microscope model BX51, while others were taken as snap shots from sca nned computerized ones. Results In the current study, 40 cases were studied. The age of patients ranged between 30 to above 70 years. 20 cases (50%) were 50 years old or less and 20 cases (50%) were older than 50 years. This study revealed that the most common type was invasive duct carcinoma (NOS) representing (82.5%) of the cases (Figs. 1,2). Concerning size, the majority were those with maximal dimension within the range of more than 2cm up to 5cm representing (67.5%) of cases. Rregarding the nuclear grade; most cases were low grade (I & II) constituting (67.5%). Concerning the nodal status, by application of TNM staging system 18, the majority of cases (62.5%), showed positive nodal status. Intraductal component was present in 30% of cases, while tumoral necrosis was detected in (12.5%) of cases. Demonstratation of clinical and histopathologic characteristics in all studied groups is tabulated in (Table 1). Considering the presence of mast cells in the peritumoral stroma, mast cells were detected in (72.5%) of the cases (Figs. 3-6), while they were absent in (27.5%) of cases. Stromal mast cells were detected in (16/20) cases at the age of 50 years or less (80%), while in patients above the age of 50 years, they were detected in (13/20) cases (65%). The correlation between age and stromal mast cells was statistically insignificant (p-value=0.477). Fig. (1): Invasive duct carcinoma (NOS) grade II (H&E x100): The view shows a prominently sclerotic stroma. The arrow points to a large vessel almost occluded with a tumor vascular embolus, attached to its wall. Fig. (2): Invasive duct carcinoma with wide micropapillary features (H&E x100): This view shows clusters of malignant ductal cells arranged in micropapillary pattern lacking fibrovascular cores. Fig. (3): Invasive duct carcinoma (c-kit x400): The stroma shows scattered c-kit positive mast cells (arrows). Fig. (4): Invasive duct carcinoma (toluidine blue oil immersion x1000): The stroma shows scattered degranulated mast cells with positive toluidine blue reaction (arrows) in a blue background.

4 48 Detection of Mast Cells in the Vicinity of Peritumoral Stroma Fig. (5): Invasive duct carcinoma (toluidine blue oil immersion x1000): The stromal mast cells show positive toluidine blue reaction (arrows) in a blue background. Fig. (6): Invasive duct carcinoma (toluidine blue oil immersion x1000): The arrow points to a toluidine blue positive mast cell in a blue background. Fig. (7): Invasive duct carcinoma with wide micropapillary features (c-kit x 200): With moderately pisitive cytoplasmic immunostaining of the tumor cells. Table (1): Clinical and histopathologic characteristics in studied groups of invasive breast carcinoma. Clinical and Histopathological Parameters N (%) Age: 50 >50 20 (50%) 20 (50%) 40 Histologic types: Invasive duct carcinoma (IDC) NOS 33 (82.5%) Lobular 5 (12.5%) Medullary 2 (5%) 40 Nuclear grade: Low grade( I &II) 27 (67.5%) High grade (III) 13 (32.5%) 40 Tumor size: T1 2 (5%) T2 27 (67.5%) T3 8 (20%) T4 3 (7.5%) 40 Nodal status: N0 15 (37.5%) N1 12 (30%) N2 5 (12.5%) N3 8 (20%) 40 Intraductal component: 12 (30%) 28 (70%) 40 Tumoral necrosis: 5 (12.5%) 35 (87.5%) 40 Fig. (8): Invasive duct carcinoma (c-kit oil immersion x1000): With moderately positive cytoplasmic immunostaining of a sheet of tumor cells as well as scattered tumor cell in the surrounding stroma. Regarding the relation between tumor type and mast cells within the surrounding stroma, 22/33 cases (66.7%) of invasive duct carcinoma cases showed stromal mast cells, while the remaining 11 cases (33.3%) showed negative results. Stromal mast cells were detected in all cases other than invasive duct carcinoma (7/7). The correlation between tumor type and the presence of stromal mast cells was statistically insignificant ( p-value =0.159) (Table 2). Table (2): Stromal mast cell infiltration versus tumor type. Type Positive Mast-cells Negative Invasive duct (66.7%) (33.3%) Others (0.0%) % (27.5%) Stromal mast cells were correlated with tumor grade and it was found that among the 27 low grade cases examined, six cases (22.2%) revealed absent mast cells, which were on the contrary present in the remaining 21 cases (77.7%). As for

5 Abdallah M. Khalil, et al. 49 high grade tumors (13 cases), five cases (38.5%) were negative for mast cells, while eight cases (61.5%) were positive. The correlation between tumor grade and the presence of mast cells in the peritumoral stroma was statistically insignificant (p-value=0.636) (Table 3). Table (3): Stromal mast cell infiltration versus tumor grade. Tumor grade Low High Cases (77.7%) (22.2%) 8 (61.5%) Mast cells 5 (38.5%) By studying the relation between the presence of mast cells and nodal status, it was found that, out of the 29 mast cell positive cases, 20 cases exhibited nodal positivity (69%), while the remaining mast cell positive cases (9/29) were node negative (31 %). On the other hand, Among the 11 mast cell negative cases, nodal positivity was detected in (5/11) of cases (45.5%) while node negative cases represented (6/11) (54.5%). The correlation between mast cell stromal infiltration and nodal status was statistically insignificant ( p- value=0.469) (Table 4). Table (4): Stromal mast cell infiltration versus nodal status. Nodal status Mast cell Count Positive Negative 20 (69%) 5 (45.5%) 9 (31%) 6 (54.5%) As for stromal mast cell infiltration versus tumoral necrosis, among the 29 mast cell positive cases, tumoral necrosis was detected only in four cases (13.7%) and absent in 25 cases (86.3%). (1/11) of the mast cell negative cases was associated with tumoral necrosis while in the remaining 10 cases tumoral necrosis was absent. The correlation between stromal mast cells infiltration and tumoral necrosis was statistically insignificant ( p-value =1.000) (Table 5). Table (5): Stromal mast cells infiltration versus tumoral necrosis. Mast cell Mast cell Count Tumoral necrosis (13.7%) (86.3%) 1 (9.1%) 10 (54.5%) Regarding c-kit immunostaining, it was found that tumor cells were positively stained in (38/40) cases (95%) (Figs. 7,8). Considering the relation of mast cell availability in the vicinity of peritumoral stroma with c-kit immunostaining of tumor cells, among the 29 of mast cell positive cases, 28 cases (96.6%) were c-kit positive, with a single negative case (3.4%), while in mast cell negative cases (10/11) were positively stained (90.9%), with a single negative case (9.1%). The correlation between stromal mast cells and tumor cell reactivity for c-kit was statistically insignificant (p-value =0.479) (Table 6). Table (6): Stromal mast cells infiltration versus c- kit expression in tumor cells. Count c-kit immunostaining Positive 28 (96.6%) 10 (90.9%) Negative 1 (3.4%) 1 (9.1%) Discussion In spite of improvement in early diagnostic methods and advances in treatment of cancer breast, mortality from this disease continues to be substantial. The identification of factors that influence disease progression and mortality is the aim of many studies in order to apply new treatment modalities. Routine pathologic evaluation remains the most critical element in determining the prognosis of patients with breast cancer. Among the most potent prognostic factors available are tumor stage, histologic grade, histologic tumor type, and lymphatic vascular invasion as well as biological factors such as ER, PR and HER2/neu [19]. Regarding the presence of mast cells in the peritumoral stroma of invasive breast carcinomas,

6 50 Detection of Mast Cells in the Vicinity of Peritumoral Stroma few studies have been done and there was a mounting evidence indicating that mast cells accumulate around tumors and they could inhibit tumor growth depending on the local stromal conditions [20,21]. Mast cells might, therefore act as a new target for the adjuvant treatment of these tumors, through selective inhibition of tumor promoting molecules, and by permitting secretion of cytotoxic cytokines [22]. We included 40 cases of invasive breast carcinoma. The mean age of the studied patients with breast carcinoma was 55 years. Considering the type of breast cancer, our study revealed that most cases (82.5%) were invasive duct carcinoma (NOS). Regarding mast cells within the peritumoral stroma, this study revealed no significant correlation between their presence and other clinicopathological variables including patient's age, tumor type, size, grade, nodal status, tumoral necrosis or c-kit immunoreactivity of adjacent tumor cells. Similarly Dabiri et al. [17], didn't find any significant relationship between mast cell presence and tumor grade. On the contrary, Aaltoma et al. [20] and Rajput et al. [21] had showed that the presence of numerous stromal mast cells was associated with good prognosis and they observed a significant correlation between mast cell presence and tumor grade as well as tubular differentiation. Also, Heidarpour et al. [23] studied the presence of mast cells in invasive duct carcinoma and they reported that the presence of mast cells was also associated to low tumor grade. These findinings might, thus be interpreted as that existence of many mast cells is an additive favorable prognostic sign in cancer breast. In lymph nodes of women with breast cancers, a higher number of mast cells was found in the non-involved axillary lymph nodes in those women with a better prognosis in a study performed by Bowers et al. [24]. Furthermore, Naik and his colleagues [25] have found more mast cells in the non-involved axillary lymph nodes in women with axillary lymph node metastasis. These findings might indicate a protective effect of mast cells, possibly exerting a cytotoxic effect on the tumor cells. The controversy in results between different studies might be attributed to that mast cells accumulation around tumors could either promote or inhibit tumor growth depending on the local stromal conditions. The presence of stromal mast cells in other malignant tumors has been of interest, but comprehensive studies are few. In colon cancer, high amounts of mast cells have been associated with lower rates of lymph node metastasis and distant metastasis [26]. In squamous cell carcinomas of the esophagus [27] and cervix [28], high numbers of mast cells in the tumors were likewise associated to both microvessel density and tumor progression. Similarly, in malignant melanomas [29] and Hodgkin lymphomas [30], mast cells have been related to an adverse clinical outcome. Regarding c-kit immunostaining, the detection of c-kit positivity in both the tumor cells and mast cells in the current study was also reported in the study done by Pittoni et al. [31] as well as Pittoni and Colombo [32] who studied c- kit expression in prostatic carcinoma and they have concluded that the common expression of c-kit by mast cells and tumor cells suggests a possible competition for the ligand stem cell factor. This latter finding might indicate that c-kit targeted therapy with tyrosine kinase inhibitors (TKIs) may ideally work against both tumor and stromal mast cells and offers the chance of curing early-stage disease. In conclusion, in this study, no significant relationship was detected between stromal mast cell infiltrates in the vicinity of peritumoral stroma and other clinicopathological criteria; this may be due to small sample size in relation to the wide scale of variables. Thus, the presence of stromal mast cells in different tumors and their precise role in carcinogenesis need to be further investigated on a wider scale of patients and using more advanced techniques, aiming at earlier diagnosis as well as application of new treatment modalities with the least drawbacks, least morbidity and longer survival. References 1- DEY S., SOLIMAN A.S., HABLAS A., SEIFELDIN I.A., ISMAIL K., RAMADAN M., EL-HAMZAWY H., WIL- SON M.L., BANERJEE M., BOFFETTA P., HARFORD J. and MERAJVER S.D.: Urban-rural differences in breast cancer incidence by hormone receptor status across 6 years in Egypt. Breast Cancer Res. Treat., 1: , 120, ELATTAR I.A., HASSAN N.M., LAMEE M.M. and ELBASMY A.: A Cancer profile at the National Cancer Institute, Egypt, Journal of Clinical Oncology, 2005 ASCO Annual Meeting Proceedings, Vol. 23. No, 16S (June 1 Supplement): 9653, DE VISSER K.E. and COUSSENS L.M.: The inflammatory tumor microenvironment and its impact on cancer development, Contrib. Microbiol., 13: , BALKWILL F. and MANTOVANI A.: Inflammation and cancer, back to Virchow, 357: , RIBATTI D., VACCA A., NICO B., CRIVELLATO E., RONCALI L. and DAMMACCO F.: The role of mast cells in tumour angiogenesis. Br. J. Haematol., 115: , NORRBY K.: Mast cells and angiogenesis. APMIS, 110: , 2002.

7 Abdallah M. Khalil, et al COUSSENS L.M., RAYMOND W.W., BERGERS G., LAIG-WEBSTER M., BEHRENDTSEN O., WERB Z., et al.: Inflammatory mast cells up-regulate angiogenesis during squamous epithelial carcinogenesis. Genes Dev., 13: , GALLI S.J., KALESNIKOFF J., GRIMBALDESTON M., PILIPONSKY A., WILLIAMS C. and TSAI M.: Mast cells as tunable effector and immunoregulatory cells: Recent advances. Annu. Rev. Immunol., 23: , GALLI S.J., NAKAE S. and TSAI M.: Mast cells in the development of adaptive immune responses. Nat. Immunol., 6: , SCHWARTZ L.B. and BRADFORD T.R.: Regulation of tryptase from human lung mast cells by heparin. Stabilization of the active tetramer. J. Biol. Chem., 261: , SAMOSZUK M., TAN J. and CHORN G.: Clonogenic growth of human breast cancer cells co-cultured in direct contact with serum-activated fibroblasts. Breast Cancer Res., 7: R274-83, SAMOSZUK M. and CORWIN M.A.: Acceleration of tumor growth and peri-tumoral blood clotting by imatinib mesylate (Gleevec). Int. J. Cancer, 106: , LIU C.L., PRAPONG W., NATKUNAM Y., ALIZADEH A., MONTGOMERY K., GILKS C.B. and VAN DE RIJN M.: Software tools for high-throughput analysis and archiving of immunohistochemistry staining data obtained with tissue microarrays. Am J. Pathol., 161: , TAVASSOLI F.A. and DEVILEE P. (Eds): World Health Organization Classification of Tumours. Pathology and Genetics of tumours of breast and female genital organs. IARC Press: Lyon, ELSTON E. and ELLIS I.O.: The Breast; Vol. 13, NY, Churchill Livingstone, p 365, TSUTSUI S., YASUDA K., SUZUKI K., TAKEUCHI H., NISHIZAKI T., HIGASHI H. and ERA S.: A loss of c- kit expression is associated with an advanced stage and poor prognosis in breast cancer. Br. J. Cancer, 94 (12): , DABIRI S., HUNTSMAN D., MAKRETSOV N., CHEANG M., GILKS B., BAJDIK C., GELMON K., CHIA S. and HAYES M.: The presence of stromal mast cells identifies a subset of invasive breast cancers with a favourable prognosis. Mod. Pathol., 17: , EDGE S.B., BYRD D.R. and COMPTON C.C. (Eds): Cancer Staging Manual, AJCC (American Joint Committee on Cancer), 7 th edition, Springer-Verlag, New York., p.347, FITZGIBBONS P. L., PAGE D. L. and WEAVER D.: Prognostic factors in breast cancer. College of American Pathologists Consensus Statement, Arch. Pathol. Lab. Med., 124 (7): , AALTOMAA S., LIPPONEN P., PAPINAHO S. and KOSMA V.M.: Mast cells in breast cancer. Anticancer Res., 13: 785-8, RAJPUT A.B., TURBIN D.A., CHEANG M.C., VODUC D.K., LEUNG S. and GELMON K.A.: Stromal mast cells in invasive breast cancer are a marker of favourable prognosis: A study of 4,444 cases. Breast Cancer Res. Treat., 107: , THEOHARIDES T.C. and CONTI P.: Mast cells: The Jekyll and Hyde of tumor growth. Trends Immunol., 25: , HEIDARPOUR M., RAJABI M. and FARKHANI H.: Mast cells in breast carcinoma. Journal of Research in Medical Sciences, Vol. 13, No. 5, 259, BOWERS H.M., J.R., MAHAPATRO R.C. & KENNEDY J.W.: s of mast cells in the axillary lymph nodes of breast cancer patients. Cancer, 43: , NAIK R., BALIGA P., BANSAL R. and PAI M.: Distribution of mast cells in the axillary lymph nodes of breast cancer patients. J. Indian Med. Assoc., 95: 606-7, TAN S.Y., FAN Y., LUO H.S., SHEN Z.X., GUO Y. and ZHAO L.J.: Prognostic significance of cell infiltrations of immunosurveillance in colorectal cancer. World J. Gastroenterol., 11: , ELPEK G.O., GELEN T., AKSOY N.H., ERDOGAN A., DERTSIZ L. and DEMIRCAN A.: The prognostic relevance of angiogenesis and mast cells in squamous cell carcinoma of the oesophagus. J. Clin. Pathol., 54: 940-4, BENITEZ-BRIBIESCA L., WONG A., UTRERA D. and CASTELLANOS E.: The role of mast cell tryptase in neoangiogenesis of premalignant and malignant lesions of the uterine cervix. J. Histochem. Cytochem., 49: , RIBATTI D., ENNAS M.G., VACCA A., FERRELI F., NICO B. and ORRU S.: Tumor vascularity and tryptasepositive mast cells correlate with a poor prognosis in melanoma. Eur. J. Clin. Invest, 33: 420-5, MOLIN D., EDSTROM A., GLIMELIUS I., GLIMELIUS B., NILSSON G. and SUNDSTROM C.: Mast cell infiltration correlates with poor prognosis in Hodgkin's lymphoma. Br. J. Haematol., 119: 122-4, PITTONI P., PICONESE S., TRIPODO C. and COLOMBO M.P.: Tumor-intrinsic and extrinsic roles of c-kit: Mast cells as the primary target of tyrosine kinase inhibitors. Oncogene, 30: , PITTONI P. and COLOMBO M.P.: The dark side of mast cell-targeted therapy in prostate cancer. Cancer Res., (4): 831-5, 2012.