The loss of NM23 protein in malignant melanoma predicts lymphatic spread without affecting survival

NM23 is considered to be a metastasis suppressor gene the role of which as prognosticator in the case of malignant skin melanoma (MM) is highly controversial due to different results on gene, and protein expressions. Accordingly, we analyzed the protein expression of NM23 in 32 primary skin melanomas with a follow-up period of 5 years minimum. We found that NM23 expression was the lowest in the thickest primary tumors (based on the % of the positive cells and the incidence of low expressor tumors) but the difference was not significant statistically due to the extreme heterogeneity of the tumors. When primary tumors were grouped according to their biological behavior (non-metastatic; lymph-node (LN) metastatic; organ and LN metastatic tumors) we observed that the lowest NM23 protein expression (based on the % of positive tumor cells as well as on the incidence of low expressor tumors) was found in the LN metastatic tumors compared to other groups (p < 0.05). The NM23 phenotype of the primary tumors remained stable in the corresponding LN metastases in the case of the 5 analyzed tumors. There was no difference in the 5-year survival between patients with low (< 50% positive cells) or high NM23 protein expressing primary tumors. Collectively, these data suggest that the NM23 protein expression in the primary tumors of MM predicted lymphatic spread but did not affect 5-year survival because it did not correlate with organ metastasis.