SMAD4 and skin squamous cell carcinoma: ERBB4 and NPM1 alterations were equally frequent, whereas APC, ATM, CDKN2A, EGFR, ERBB2, FGFR2, FGFR3, MET, MPL, NOTCH1, PDGFRA, RB1, RET, SMAD4, SMARCB1, SMO, and TP53 alterations were more frequent in cSCC+ than in cSCC- cases.