Successful Remission of Advanced Basosquamous Cell Carcinoma with Cemiplimab Monotherapy

Summary: Basosquamous cell carcinoma (BSC) is a rare and aggressive subtype of non-melanoma skin cancer that exhibits clinical and histologic features of both basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). Despite its higher rate of recurrence and potential for metastasis, current treatment guidelines are limited and tend to mirror that of BCC. Cemiplimab, a programmed death receptor-1 blocking antibody, has recently been approved for first line treatment of SCC and second line for BCC. We describe two cases where successful remission of BSC was achieved with cemiplimab in an effort to highlight an alternative therapeutic approach. To our knowledge, there have only been a few cases of BSC remission with cemiplimab monotherapy previously reported. The first is an 82-year-old male who presented with significant tissue loss and ulceration of the left nasal cavity and cheek that reportedly arose from a lesion present for 20 years for which he had never sought medical treatment. A biopsy confirmed infiltrative basal cell carcinoma staged at cT3N0 and treatment with vismodegib was initiated. Despite dramatic improvement, side effects necessitated a decreased dose and he developed disease recurrence. Treatment was switched to sonidegib but his facial ulceration continued to worsen. A repeat biopsy revealed invasion of poorly differentiated squamous cell carcinoma and he began cemiplimab infusions at 3 week intervals. The patient experienced rapid clinical improvement and computed tomography (CT) imaging after 8 infusions revealed decreased tissue involvement with repeat imaging after 12 infusions confirming disease stability. The second patient is an 81-year-old male who initially presented with a recurrent basal cell carcinoma of the left postauricular sulcus. Since then, the patient has undergone multiple Mohs procedures, radiotherapy treatment and, despite initial improvement on vismodegib, the lesion ultimately recurred with evidence of conversion to basosquamous cell carcinoma. A wide local excision with left partial auriculectomy and partial parotidectomy revealed infiltration of the left parotid gland with perineural invasion. The tumor was staged at pT3 and adjuvant radiotherapy was completed. At follow up six months later, the patient had developed near complete left facial paralysis and a biopsy confirmed recurrence. Advancement of disease precluded further surgical intervention so treatment was initiated with cemiplimab infusions at 3 week intervals. Full body fluorodeoxyglucose (FDG)-positron emission tomography (PET) performed after 4 and 8 infusions revealed complete remission. Given its relatively high rate of metastasis and recurrence, early and effective treatment of BSC is imperative. In patients with recurrent and destructive BSCs, treatment with cemiplimab should be considered.