Clinical Next-Generation Sequencing Panels Reveal Molecular Differences Between Merkel Cell Polyomavirus-Negative Merkel Cell Carcinomas and Neuroendocrine Carcinomas.

High tumor mutational burden and UV signature, as well as the presence of NF1 and PIK3CA mutations, are supportive of MCPyV-negative MCC, whereas KEAP1, STK11, and KRAS mutations are supportive of NEC in the appropriate clinical context. Although rare, the presence of a gene fusion is supportive of NEC.