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

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.

However, its action on squamous cell carcinoma (SCC) is unknown. We present three SCC cases developed into BCC in vismodegib-treated patients.

We have described three cases of patients developing SCC during treatment by vismodegib for BCC.

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.

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.

In practice, any dissociated response of a BCC to vismodegib should be biopsied.