Clinical implications of distinct metastasizing preferences of different melanoma subtypes.

BACKGROUND: The incidence and mortality of malignant melanoma have been rising during the past decades, the latter being due to the high invasion capacity and the metastatic potential of melanoma cells to distant organs. OBJECTIVE: We investigated the distribution pattern of melanoma metastases taking into account different clinicopathological subtypes of melanoma. METHODS: We studied 310 stage IV (AJCC 2009) melanoma patients retrospectively with regard to potential correlations between frequency and occurrence of metastasis and the genetic background and pathological/clinical melanoma subtypes. For all patients, the time to distant metastasis (TTDM) and the distribution patterns of metastases were analyzed and correlated to the median survival time. RESULTS: Superficially Spreading (SSM) and Nodular melanomas (NMM) spread to the brain more frequently than Acrolentiginous (ALM) and Mucosal (MM) melanomas (p = 0.0012). The preference to affect the skeleton was significantly higher for ALM and MM in comparison to SSM and NMM (p = 0.0049). Lentigo maligna (LMM) tumors showed a significantly lower metastatic spread to distant lymph nodes (p = 0.0159). BRAF mutant versus wildtype tumors showed no significant differences concerning localization of metastasis but patients with BRAF mutant tumors were significantly younger at primary diagnosis and had a significantly shorter stage IV survival (p = 0.0106). CONCLUSION: This study shows a clear distinction of melanoma subtypes with regard to metastasizing preferences. Further knowledge about melanoma subtype specific characteristics, including molecular markers predictive of homing preferences, may help to understand and manage this heterogeneous disease in terms of prognosis and follow-up procedures.

Sinonasal, genital and acrolentiginous melanomas show distinct characteristics of KIT expression and mutations.

KIT aberrations predict the outcome of targeted therapies in acrolentiginous (ALM) and mucosal (MM) melanoma patients. KIT immunoreactivity and mutation status was assessed in 41 ALM and 25 MM patients. Of these, 19 ALM and 15 MM patients had matched primary and metastatic lesions. P-ERK was investigated in a subset of 9 ALM and 7 MM matched primary/metastatic pairs by immunohistochemistry. Heterogeneous KIT immunoreactivity was observed in both primary and metastatic lesions. Mutations were present in four of 41 ALM (10%) and five of 25 MM (20%) patients. Only vulvar mucosal samples carried KIT mutations in contrast to sinonasal lesions (p = 0.0109). In KIT-mutated tumours, the mutations were present in KIT expressing as well as KIT negative cells, as shown by Laser Capture Microdissection (LCM). P-ERK expression was preferentially found in metastases. KIT mutations predict treatment outcome with KIT inhibitors. Therefore, especially vulvar melanoma patients should be screened for activating KIT mutations.