ALK is frequently phosphorylated in Merkel cell carcinoma and associates with longer survival

Abstract

Merkel cell carcinoma (MCC) is a rare skin cancer with only limited therapeutic options for advanced disease. We previously showed that oncogene ALK is frequently expressed at the RNA level in MCC and further that ALK positivity by immunohistochemistry is frequent and correlates strongly with Merkel cell polyomavirus (MCPyV) positivity. In this study, we investigated whether ALK receptor is active in MCC tumor samples and MCC cell lines, and whether ALK would be a prospective treatment target in MCC. We utilized tissue microarrays constructed from 136 primary MCC tumor samples as well as nine previously established MCC cell lines to determine the presence of ALK and phosphorylated ALK (p-ALK) via immunohistochemistry. Almost half of the analyzed MCC tumors displayed ALK phosphorylation (47.8%). Analysis of MCC tumor samples revealed that the presence of p-ALK correlated to MCPyV positivity, younger age, nonexistence of metastases at diagnosis and ultimately to better MCC-specific survival. In contrast to MCC tumor samples only two out of nine MCC cell lines showed only low ALK phosphorylation by immunohistochemistry. Our study reveals clear disparity in ALK activity between patient derived tumors and cell line samples and therefore, more advanced disease models such as xenografts are necessary to resolve whether ALK is a useful treatment target in MCC.

Clinical-Pathological Evaluation and Prognostic Analysis of 228 Merkel Cell Carcinomas Focusing on Tumor-Infiltrating Lymphocytes, MCPYV Infection and ALK Expression

“…The expression and role of ALK in MCC is of emerging interest: only few reports have highlighted a positive correlation between ALK and viral status [13,20,29,59], although the underlying mechanism has not been clarified, yet [22]. Along with our results, this suggests that MCPyV infection could play a role in promoting ALK overexpression in neoplastic cells [26]. Interestingly, we found increasing ALK tumor expression to be an independent indicator of progressively shorter DFI by multivariate analysis, suggesting strong ALK expression to be associated with a more aggressive clinical course.…”

“…We were surprised to notice the opposite finding in a recent paper by Jaatinen et al, who observed a better survival in patients showing moderate/ high ALK and phosphorylated ALK (p-ALK) tumor expression [26]. Such divergent results could be related to the use of a tissue microarray-based technical procedure in Jaatinen's study [26] and/or to tumor heterogeneity which requires further investigations, in order to open the way to novel therapeutic approaches [68].…”

“…MCPyV status was assessed in 178 cases and interpreted according to Moshiri et al [12]; cases were considered negative when weak staining was observed in < 1% of tumor cells. ALK staining was performed in 155 cases and scored according to both the percentage of positive tumor cells and their staining intensity as negative, low, intermediate or high (partially based on previous literature data [20,26,29]). Specifically, the reaction was considered negative when staining was observed in < 1% of tumor cells; low when very weak to moderate staining intensity was observed in < 25% of tumor; intermediate when weak to moderate staining intensity was observed in > 25% of tumor cells, or when strong staining intensity was observed in < 25% of tumor cells; high when strong staining intensity was observed in > 25% of tumor cells.…”

“…Stratifying all cases into four distinct groups according to viral status and presence of a brisk pattern of TILs, the combination of negative viral status and absent/non-brisk TILs correlated with a significantly worse prognosis (p = 0.001), whereas patients with MCPyV + /brisk-TILs tumors showed a longer survival (p = 0.05). ALK expression was analyzed in respect to patient's DSS both as a continuous variable based on staining intensity and as a discrete variable (negative versus positive and negativeweak versus intermediate-high), according to literature data [26]. No significant correlations with DSS were detected, neither in univariate nor in multivariate analysis.…”

“…In addition, cKIT, PDGFRA, ALK and EGFR represent only some of the biomarkers examined in MCC in order to better define its pathogenesis [20][21][22][23][24][25]. In particular, ALK tumor expression has been reported in MCC and was recently shown to correlate with viral status as well as a longer survival [20,22,26].…”