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

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, Kaposi'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.