Mast cells in cutaneous tumors: innocent bystander or maestro conductor?

Abstract Background Evidence favoring a critical role for mast cells ( MC ) in cutaneous malignancies is conflicting. Methods Using the immunohistochemical stain tryptase, MC counts were performed in the following tumor categories: epithelial (basal cell carcinoma [ BCC ]: nodular [ N ], n = 10, infiltrative [I], n = 10; squamous cell carcinoma [ SCC ]: well differentiated [ W ], n = 9, moderate/poorly differentiated [ MP ], n = 15); melanocytic (intradermal nevus, n = 10, malignant melanoma in situ [ MMIS ], n = 8, invasive melanoma, n = 15); vascular (hemangioma [ HEM ], n = 11, K aposi's sarcoma [ KS ], n = 14, angiosarcoma [ AS ] n = 8); and fibrohistiocytic (dermatofibroma [ DF ], n = 7, atypical fibroxanthoma [ AFX ], n = 5, dermatofibrosarcoma protuberans [ DFSP ], n = 5). MC (intra‐ and peritumoral) were expressed as cells per 10 high‐power fields. Results Mean MC counts were: BCCN 166.30; BCCI 130; SCCW 167.22; SCCMP 133.80; nevus 156.40; MMIS 93; MM radial growth phase 73.86; MM vertical growth phase 82.13; HEM 165.18; KS 120.57; AS 168.13; DF 247.86; AFX 280.20; and DFSP 83.60. Using a one‐way analysis of variance, statistically significant differences were observed in the following pairs: AFX and DF vs. DFSP , nevus vs. melanoma, AS and HEM vs. KS . Conclusions Our findings appear to point towards a dichotomous role for mast cells in fibrohistiocytic and vascular neoplasms and argue against their preferential recruitment in epithelial malignancies and malignant melanoma. The value of mast cell counts as a prognostic index appears to be limited in most cutaneous malignancies.