NTRK1 and Merkel cell skin cancer: RT-PCR of this metastatic MCPyV-positive MCC detected expected products for both full-length fully spliced TrkA and full-length alternatively spliced Δ exon 6–7 TrkAIII, with the 1112-bp exon 1–8 fully spliced TrkA and 836-bp exon 1–8 and 139-bp Δ exon 6–7 TrkAIII RT-PCR products confirmed by DNA sequence comparison to the TrkAI splice variant reference sequence NM_001012331.2, confirming alternative Δ exon 6–7 TrkAIII mRNA splicing.