Prediction of metastases in melanoma patients with positive sentinel node: histological and molecular approach

It is now established that sentinel node (SN) biopsy is a minimally-invasive procedure that accurately indicates the regional nodal status. In our institute, 14 consecutive patients had only one node micrometastases after elective lymph node dissection or positive SN for primary cutaneous melanoma. These 14 patients could be clearly divided into two groups: (i) patients who developed distant metastases or in-transit metastases (metastasized group); and (ii) and patients who remains free from metastases (non-metastasized group). The purpose of this study was to identify the histological and molecular factors that might predict the further dissemination beyond the SN. We assessed the maximum depth from the capsule to the deepest melanoma cells and the maximum diameter of melanoma nests in the lymph nodes as histological parameters and also evaluated the quantitative expression of tyrosinase mRNA as a molecular approach. The mean maximum depth and the maximum diameter were significantly smaller in the metastasized group than those in the non-metastasized group. Tyrosinase mRNA expression was strongly correlated with the histological tumor burden. Tyrosinase mRNA expression was higher in the former group than that in the latter group but there were no significant differences between them. Melanoma patients with small micrometastases (<0.5 mm deep, <1 mm in diameter) and a low level of tyrosinase mRNA had less chances for hematogenous metastases via lymph nodes.