Assessment of melanoma-initiating cell markers and conventional parameters in sentinel lymph nodes of malignant melanoma

Sentinel lymph node (SLN) biopsies have widely been used for the detection of occult LN metastasis of malignant melanoma (MM). In addition to conventional biomarkers, we assessed the diagnostic and prognostic significance of melanoma-initiating cell (MIC) markers in SLNs of MM. We examined the expressions of gp100, MARTI-1 and tyrosinase mRNA for routine diagnosis and those of ABCB5, CD133, nestin, KDM5B, NGFR and RANK mRNA as MIC markers. The presence of micrometastasis was confirmed immunohistochemically using antibodies to S-100, HMB-45, MARTI-1, and tyrosinase. Discordance between immunohistochemical and molecular data was observed in 14 of 70 (20.0%) patients, among whom five (7.1 %) were positive for only molecular markers; two of these five patients tested positive for micrometastasis by repeated immunohistochemical stainings. The quantitative expression levels of gpl00, MARTI-1, and tyrosinase mRNA were significantly higher in the metastatic LNs; the cut-off values remain to be elucidated. ABCB5 mRNA expression was detected more frequently in the metastatic SLNs (p < 0.05) and in the group of patients with recurrence. To make a definite diagnosis of metastasis, we still need a combination of immunohistochemical and molecular probes. ABCB5 might be a suitable molecular marker for the detection of melanoma-initiating cells in SLNs.