In other cancers, immunohistochemical detection of TrkA phosphorylation has been shown to predict poor outcome and an aggressive phenotype in melanoma and to predict response to Larotrectinib therapy in cancers driven by Trk fusion oncogenes [16–18, 36], suggesting that the detection of TrkAIII expression and phosphorylation in MCPyV positive MCCs may eventually provide similar information of diagnostic and therapeutic significance. This evidence concerns the gene NTRK1 and cancer.