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.

Detecting BRAF Mutations in Formalin-Fixed Melanoma: Experiences with Two State-of-the-Art Techniques.

BACKGROUND: Melanoma is characterized by a high frequency of BRAF mutations. It is unknown if the BRAF mutation status has any predictive value for therapeutic approaches such as angiogenesis inhibition. PATIENTS AND METHODS: We used 2 methods to analyze the BRAF mutation status in 52 of 62 melanoma patients. Method 1 (mutation-specific real-time PCR) specifically detects the most frequent BRAF mutations, V600E and V600K. Method 2 (denaturing gel gradient electrophoresis and direct sequencing) identifies any mutations affecting exons 11 and 15. RESULTS: Eighteen BRAF mutations and 15 wild-type mutations were identified with both methods. One tumor had a double mutation (GAA) in codon 600. Results of 3 samples were discrepant. Additional mutations (V600M, K601E) were detected using method 2. Sixteen DNA samples were analyzable with either method 1 or method 2. There was a significant association between BRAF V600E mutation and survival. CONCLUSION: Standardized tissue fixation protocols are needed to optimize BRAF mutation analysis in melanoma. For melanoma treatment decisions, the availability of a fast and reliable BRAF V600E screening method may be sufficient. If other BRAF mutations in exons 11 and 15 are found to be of predictive value, a combination of the 2 methods would be useful.

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.

A proliferative melanoma cell phenotype is responsive to RAF/MEK inhibition independent of BRAF mutation status.

Oncogenic mutations within the MAPK pathway are frequent in melanoma, and targeting of MAPK signaling has yielded spectacular responses in a significant number of patients that last for several months before relapsing. We investigated the effects of two different inhibitors of MAPK signaling in proliferative and invasive melanoma cell cultures with various mutations in the MAPK pathway. Proliferative melanoma cells were more susceptible to pathway inhibition than invasive phenotype cells, irrespective of BRAF mutation status, while invasive phenotype cell response was dependent on BRAF mutation status. Critically, MAPK pathway inhibition of proliferative phenotype cells resulted in acquisition of invasive phenotype characteristics. These results show that melanoma cell phenotype is an important factor in MAPK pathway inhibition response. This suggests that while current therapeutic strategies target proliferative melanoma cells, future approaches should also account for the invasive phenotype population.