Lamin subtype expression in Merkel-cell carcinoma: its relation to polyomavirus infection and tumor metastasis

Merkel-cell carcinoma (MCC) is known for its high metastatic potential. Studies in several tumor types have proposed a role for up- or downregulation of nuclear A- and B-type lamins in facilitating the process of invasion and metastasis, but such studies are lacking for MCC. Therefore, lamin expression levels were examined in 38 tissue samples from 28 patients with MCC using immunohistochemistry. The series comprised primary tumors and different metastases and both Merkel cell polyomavirus (MCPyV) positive and MCPyV-negative cases. This study revealed that primary MCC tumors express variable, but mostly low levels of A-type lamins, while the B-type lamins are overall highly expressed. No obvious differences in lamin expression were observed between the MCPyV-positive and MCPyV-negative cases. A generally higher A-type lamin expression was detected in MCC metastases, although comparison of primary tumors versus metastases from the same patients showed either no change or up- or downregulation of A-type lamins. Normal Merkel cells were found to express both A- and B-type lamins. Conclusively, our data suggest a flexible A-type lamin expression in the process of MCC carcinogenesis and metastasis, which is an important finding regarding the aggressiveness of MCC and in the debate about the cellular origin of MCC.