Low numbers of tryptase+ and chymase+ mast cells associated with reduced survival and advanced tumor stage in melanoma.

The role of mast cells in cutaneous melanoma remains unclear. Tryptase and chymase are serine proteinases and major proteins in mast cell secretory granules. Therefore, this study aimed to investigate the presence of tryptase and chymase mast cells in benign and malignant cutaneous melanocytic lesions and in lymph node metastases of melanomas. The presence of positively stained mast cells was correlated with clinicopathological characteristics in invasive melanomas. Paraffin-embedded sections of 28 benign (13 intradermal, 10 compound, and five junctional nevi) and 26 dysplastic nevi, 15 in-situ melanomas, 36 superficially (pT1, Breslow's thickness<1 mm), and 49 deeply (pT4, Breslow's thickness>4 mm) invasive melanomas and 30 lymph node metastases were immunohistochemically stained for mast cell tryptase and chymase, and immunopositive cells were counted using the hotspot counting method. The mean count of tryptase and chymase mast cells was lower in invasive melanomas compared with in-situ melanomas and dysplastic and benign nevi. In deeply invasive melanomas, the difference was statistically significant compared with dysplastic nevi (P=0.003 for tryptase and P=0.009 for chymase) and in-situ melanomas (0.043 for tryptase). Low numbers of tryptase mast cells were associated with poor overall survival (P=0.031) in deeply invasive melanomas and with a more advanced stage (T1b, P=0.008) in superficially invasive melanomas. Low numbers of chymase mast cells were associated with microsatellites (P=0.017) in deeply invasive melanomas. The results suggest that these serine proteinases of mast cells may be protective in the pathogenesis of melanoma.