Development of squamous cell carcinoma into basal cell carcinoma under treatment with Vismodegib

Background Basal cell carcinoma ( BCC ) is the most common cancer in humans. Vismodegib, a Hedgehog pathway inhibitor, has proved its effectiveness in treating non‐resectable advanced BCC . Aim However, its action on squamous cell carcinoma ( SCC ) is unknown. We present three SCC cases developed into BCC in vismodegib‐treated patients. Material and methods We have described three cases of patients developing SCC during treatment by vismodegib for BCC . Results Patient 1 was treated with vismodegib for five facial BCC . Due to the progression of one of the lesions at month 3 (M3), a biopsy was performed and showed SCC . Patient 2 was treated with vismodegib for a large facial BCC . A biopsy was performed at M2 on a BCC area not responding to treatment and showed SCC . Patient 3 was treated with vismodegib for a BCC on the nose. Due to vismodegib ineffectiveness, a biopsy was performed and showed SCC . Discussion Two similar cases have been described in the literature. This could be due to the appearance of the squamous contingent of a metatypical BCC or to the squamous differentiation of stem cells through inhibition of the hedgehog pathway. Conclusion In practice, any dissociated response of a BCC to vismodegib should be biopsied.