[Synergistic effect of anti-PD1 immunotherapy then radiotherapy in advanced basal cell carcinoma]

Introduction: Vismodégib is the first-line treatment for non-operable or metastatic locally advanced basal cell carcinomas (LABCC), although complete response is rare and adverse effects are common. Immune checkpoint inhibitors are currently being evaluated in this indication. Herein we report a case of LABCC that responded dramatically to sequenced "immunotherapy then radiotherapy".

Observation: A 47-year-old male presented peri- and intra-orbital infiltrative LABCC that had been present for more than 10 years. After an initial response to vismodégib, further disease progression resulted in the introduction of successive lines of treatment (radiotherapy, platinum salts and itraconazole) without any significant response. Compassionate treatment with pembrolizumab was initiated. After eight courses, major clinical progression occurred with intraoral extension responsible for respiratory discomfort. Following withdrawal of pembrolizumab, high-energy radiotherapy was started with a spectacular response, both clinically and in terms of imaging.

Discussion: The efficacy of "radiotherapy-immunotherapy" sequencing in melanoma has been reported, due in particular to the abscopal effect and radiosensitisation. In our case, where the sequence was inverted, immunotherapy may have enhanced the effects of radiotherapy through "immunosensitisation", whereas radiotherapy alone had previously been ineffective. This observation underlines the potential value of these treatments, either combined or in sequence, and their synergistic effects and optimal association require further evaluation.