Efficacy of cetuximab after immunotherapy (IO) in advanced cutaneous squamous cell carcinoma (CSCC).

Abstract

9562 Background: Anti-PD1 (aPD1) monotherapy with cemiplimab-rwlc or pembrolizumab is now considered standard of care for first-line management of advanced CSCC not amenable to surgery or curative radiotherapy. Previously chemotherapy or anti-EGFR agents were commonly used for these patients albeit with modest efficacy and limited duration of response. In prospective evaluation, the overall response rate (ORR) to cetuximab was 28% with disease control rate (DCR) of 69% at 6 weeks. The efficacy of second-line treatment following primary or acquired resistance to aPD1 therapy is not known. We investigated the activity of cetuximab in patients who progressed on previous IO therapy. Methods: We performed a single institution retrospective review from 9/28/18 (US approval date of cemiplimab-rwlc for CSCC) through 11/30/20 of patients with locally advanced or metastatic CSCC who received cetuximab after prior IO therapy. We identified patients who received cetuximab either immediately following IO therapy (cohort A) or as a subsequent line not immediately following IO therapy (cohort B). Primary endpoint was ORR with secondary endpoints of DCR, survival and toxicity. Median follow-up and survival times were calculated using the Kaplan-Meier method. Results: Thirteen patients, median age 72 years (62-82), all Caucasian, and 11 males (85%) were included in this study. Eleven pts received cetuximab immediately post-IO progression; two had additional intervening therapy post-IO before receiving cetuximab. Three patients received concurrent radiotherapy (palliative or definitive) with cetuximab. The ORR to cetuximab was 54% (7/13) including 1 complete and 6 partial responses. The cumulative 6-month DCR was 77%. All responses were observed in cohort A; both patients in cohort B had progressive disease as best response. Six of 7 initial responses are ongoing, including 3 in whom cetuximab was discontinued. At a median follow-up of 9.1 months, the median PFS has not been reached for the entire cohort. There were no unanticipated toxicities to cetuximab with rash (77%) and hypomagnesemia (54%) being the most common adverse events. Conclusions: In advanced CSCC, cetuximab used immediately after progression on aPD1 therapy yields notably higher and durable overall response than previously reported in the pre-IO therapy era. If validated in a larger dataset, this should be the preferred therapy for second-line treatment in advanced CSCC. Further exploration into the mechanism of this high efficacy of anti-EGFR therapy post aPD1 therapy is warranted.