Squamous Change in Basal-Cell Carcinoma with Drug Resistance

In a 62-year-old woman with advanced basal-cell carcinoma who was treated with vismodegib, a recurrent mass was identified as a squamous-cell carcinoma that shared genetic features with the primary basal-cell tumor. To the Editor: Basal-cell carcinomas are driven by activation of the hedgehog signaling pathway, commonly through mutations in genes encoding patched 1 protein ( PTCH1 ) or smoothened, frizzled class receptor ( SMO ). Vismodegib inhibits SMO and is active in advanced basal-cell carcinomas. However, more than 50% of such lesions develop resistance to vismodegib, commonly through acquiring mutations in SMO . 1 – 3 Several cases of squamous-cell carcinomas arising from the same tumor bed as the original basal-cell lesion during vismodegib therapy have been reported. 4 However, it is unclear whether the squamous-cell lesion was related to the basal-cell clone or . . .