Melanoma Biomarker Expression in Melanocytic Tumor Progression: a Tissue Microarray Study

Background: The elucidation of protein biomarkers that are differentially expressed in human melanocytic tumors during tumor progression may lead to the identification of therapeutic targets and novel diagnostic tests. In a meeting chaired by Dr Mihm, a list of biomarkers of interest in melanoma was compiled. The specialized programs of research excellence (SPORE) in skin cancer developed a melanocytic tumor progression tissue microarray (TMA) to evaluate these candidate biomarkers. In addition to markers reported elsewhere, we evaluated c-Kit, MITF, MART1, HMB-45 and bcl-2.

Methods: The TMA contains 480 cores of benign nevi, primary cutaneous melanoma and melanoma metastases. Immunohistochemical detection of melanoma biomarkers, including c-Kit, MITF, MART-1, HMB-45 and bcl-2 was performed.

Results: Intense nuclear staining for MITF protein was observed in 83% of nevi, 56% of primary melanomas and 23% of metastases. Bcl-2 expression was reduced with progression to metastasis (detected in 86, 89 and 52% of nevi, primaries and metastases, respectively), contrary to MART-1, which showed no differential expression (74, 85 and 84%). HMB-45 was observed in 18% of nevi and most (72 and 75%) primary melanomas and metastases. c-Kit protein increased with progression from nevi to primary tumor (10 and 77% of cases, respectively) and was decreased in metastases (26% of cases).

Conclusions: Through a collaboration of the Skin SPOREs sponsored by the Organ Systems Branch of the National Cancer Institute (NCI), we identified a list of melanoma biomarkers of interest, developed a melanocytic tumor progression TMA and completed a coordinated analysis of these biomarkers. This TMA has served as a powerful validation tool for newly identified and known melanoma biomarkers by revealing trends in expression during tumor progression and by confirming the heterogeneity of biomarker expression in cutaneous melanocytic tumors.