Transformation of facial basal cell carcinoma to squamous cell carcinoma following vismodegib

Objective(s) Vismodegib, a unique hedgehog pathway inhibitor, has been demonstrated to be effective in the treatment of non-operable and metastatic basal cell carcinoma (BCC). While effective, concerns regarding its role in the development of cutaneous squamous cell carcinoma (CSCC) remain. The primary objective is to describe a unique case of locally advanced BCC of the face and subsequent transformation to CSCC following treatment with vismodegib. Methods Case report. Results A 64-year-old Caucasian female presented with a 3-year history of a progressive and erosive lesion involving the entirety of her forehead with involvement of the left medial canthus and upper eyelid. Biopsies performed at the periphery of the lesion demonstrated superficial and nodular BCC. As surgical management would result in significant morbidity, the patient elected for treatment with oral vismodegib, 150 mg daily, with curative intent. Dramatic tumor response was experienced over an 18-month period; however, surveillance MRI demonstrated concern for tumor progression at the periphery of the mass without evidence of intracranial extension or metastases. Subsequent biopsies at the superior and left supraorbital margins demonstrated invasive SCC. Following immunohistochemistry analysis, intravenous nivolumab, 480 mg monthly was initiated; the patient remains progression-free after 18 months of therapy. Conclusion This case highlights the importance of close surveillance in patients treated with vismodegib for non-operable BCC. Serial biopsies of new or suspicious appearing tumors should be performed given the potential for CSCC transformation.