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

Evidence favoring a critical role for mast cells (MC) in cutaneous malignancies is conflicting.

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.

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.

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.