Genetic evidence of a sarcomatoid transformation in Merkel cell carcinoma

Analyses of combined Merkel cell carcinomas with neuroblastic components suggests that loss of T antigen expression in Merkel cell carcinoma may result in cell cycle arrest and neuroblastic transdifferentiation

“…Individual genetic investigation of the two tumor components in such cases revealed a generally common genetic background, demonstrating that the MCC component usually derives from the squamous cell carcinoma component, demonstrating the epithelial origin of virus-negative MCCs [22,43,44]. In these tumors, the MCC component might even experience sarcomatoid transformation [24], explaining the existence of rare combined tumors with both squamous and sarcomatous differentiation [19]. In contrast, MCPyV-positive combined MCCs are very rare and seem not to occur in combination with SCCs, but have been described in association with benign adnexal tumors [21,23,[66][67][68].…”

“…The so-called combined MCCs found in association with a tumor of divergent differentiation [18,19] are a distinctive subset of MCCs accounting for about 10% of cases [20,21]. These combined MCCs are almost never related to MCPyV integration [19,22], mostly consist of an MCC with a squamous cell carcinoma component [20,22], while glandular, sarcomatoid or adnexal differentiation are also observed but rare [19,23,24]. MCCs combined with a tumor consisting of cells with an immature neuronal, a so-called 'neuroblastic' phenotype, have been reported so far only three times [19,25,26].…”