Assessing Treatment Response to PD-1 Inhibitors in Cutaneous Squamous Cell Carcinoma: Real-World Challenges

Cutaneous squamous cell carcinoma (cSCC) is a common nonmelanoma skin cancer primarily driven by chronic sun exposure and advanced age. Standard treatments include wide local excision, Mohs surgery, and radiotherapy, with advanced cases often managed with chemotherapeutics. PD1 inhibitors like cemiplimab and pembrolizumab are FDA-approved treatments that have shown efficacy in locally advanced or metastatic cSCC not amenable to surgery or radiation.

This study evaluated clinical responses to these inhibitors using RECIST 1.1 criteria through direct visual examination, addressing the applicability of the criteria in real-world clinical practice.

A cohort of 12 patients with cSCC treated at Duke University with cemiplimab or pembrolizumab was identified through the DeDUCE database using ICD-10 codes. Clinical responses were determined using RECIST 1.1 and modified WHO criteria and compared against clinical-based assessments.

Results indicated varied responses: seven patients with progressive disease (PD), two with stable disease (SD), and three with complete response (CR). Challenges included distinguishing true progression from reactive conditions like erosive pustular dermatosis (EPD) and pseudoprogression as well as evaluating partial responses in ulcerated lesions, which are not defined within the criteria. Radiologic findings often required corroboration with clinical evaluations to avoid misclassification.

Accurate clinical determination of cSCC response to PD-1 inhibitors is complex, requiring multidisciplinary approaches and meticulous wound care. Incorporating these clinical nuances into revised response criteria would enhance treatment decision-making, balancing the risks of premature discontinuation against prolonged ineffective therapy.