Decreased tumor-infiltrating lymphocytes in nodular melanomas compared with matched superficial spreading melanomas

Melanoma causes over 9000 deaths annually in the USA. Among its subtypes, nodular melanoma leads to a disproportionate number of fatalities compared with superficial spreading melanoma, the most common subtype. Recent breakthroughs in melanoma research have indicated a strong connection between melanoma virulence and the immune system. We hypothesize that the aggression of nodular melanoma may, in part, be because of decreased recognition by the immune system, as represented by a decreased presence of tumor-infiltrating lymphocytes (TILs), compared with its superficial spreading counterpart. Indeed, TILs on a primary melanoma have been used as a marker for immune response and have prognostic value for survival and sentinel lymph node status. After matching melanoma cases by age, sex, and Breslow thickness, we found significantly fewer TILs in nodular melanomas than in superficial spreading melanomas. This association was prominent in thin (≤2 mm) melanomas and was no longer significant in thick (>2 mm) melanomas. In addition, this difference in TILs was only present in men and not in women. Our finding suggests that nodular melanomas are more frequently associated with absent TILs, providing an avenue for further investigation into differences in immunogenicity of the primary melanoma and whether they underlie the unique virulence of nodular melanoma.