PD-1 Blockade With Concurrent Radiotherapy for Locally Advanced Inoperable Cutaneous Squamous Cell Carcinoma.

INTRODUCTION: For patients with locally advanced cutaneous squamous cell carcinoma (LA-cSCC), radiotherapy alone (RT) is often the only treatment option with modest tumor response. We report the outcomes of using combination of programmed cell death protein-1 (PD-1) inhibitor and RT in the treatment of inoperable LA-cSCC. The study presents the efficacy and safety data for the patients with LA-cSCC treated with this combination. METHODS: During the period 2018-2020, a total of 7 patients with biopsy proven inoperable LA-cSCC were treated with combination of PD-1 inhibitor cemiplimab and concurrent RT (Cem-RT). The patients were followed up for safety and efficacy of the Cem-RT regimen and the primary endpoints were objective tumor response and toxicity. RESULTS: The median age of patients was 68 years (range, 64-94). All patients had ECOG performance score 0-1. Six patients initially received cemiplimab and concurrent RT was added to PD-1 inhibitor when there was an inadequate therapeutic response. One patient received concurrent Cem-RT. RT with PD-1 antibody was well tolerated. Six patients developed grade ≤2 dermatitis and 1 patient (patient no. 3) developed acute grade 3 skin reaction. During the post-RT follow up, 3 patients discontinued cemiplimab due to significant toxicities. At the time of reporting , 5 patients remain in complete remission. One patient developed lung metastasis and is currently receiving best supportive care. CONCLUSIONS: The Cem-RT combination was safe and well tolerated with significant tumor response suggesting Cem-RT may be a viable therapeutic option for LA-cSCC. Our hypothesis generating data support the rationale for future prospective studies.