PIK3CA and Merkel cell skin cancer: In VN-MCC, we observed an enrichment of SEs associated with genes related to cell signaling pathways, especially TGF-β (Figure 1, C and D, and Supplemental Figure 1, B and C), consistent with aberrant signaling from reported genetic alterations of RB1, TP53, PIK3CA, and NOTCH1/2 (10, 11).