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Soo Park, MD
Soo Park, MD
Posted: Friday, October 24, 2025
Based on the STAMP (ECOG-ACRIN EA6174) trial, treatment with the PD-L1 inhibitor pembrolizumab resulted in a trend toward improved relapse-free survival and significantly prolonged distant metastasis–free survival in patients with resected Merkel cell carcinoma. These findings from the first phase III report of adjuvant immunotherapy in this clinical context were presented by Janice M. Mehnert, MD, of NYU Langone Health’s Perlmutter Cancer Center, and colleagues during the European Society for Medical Oncology (ESMO) Congress 2025 (Abstract LBA56).
“This is much-needed good news for people who are living with [this] highly aggressive cancer...,” commented Dr. Mehnert in an ECOG-ACRIN press release.
Patients with resected Merkel cell carcinoma (stage II–IV, stage I without sentinel lymph node biopsy) were randomly assigned in a 1:1 ratio to receive adjuvant pembrolizumab (200 mg every 3 weeks for 17 doses; n = 147) or observation (n = 146). They were stratified by disease stage and intended radiation therapy.
The final analysis showed numerically higher relapse-free survival with pembrolizumab vs observation (hazard ratio [HR] = 0.80; P = .105). With a median follow-up of 40 months, the 1- and 2-year relapse free survival rates were 83% and 73% with pembrolizumab and 71% and 66% with observation, respectively. Distant metastasis–free survival was found to be significantly higher with pembrolizumab (HR = 0.58; P = .032). In patients who did not undergo adjuvant radiation therapy (pembrolizumab arm: n = 79; observation arm: n = 80), relapse-free survival was numerically higher for those treated with pembrolizumab (HR = 0.62; P = .056). Mature overall survival data have not yet been reported.
Safety events appeared to be consistent with the known toxicities of pembrolizumab and radiation therapy. Treatment (ie, pembrolizumab and/or radiation therapy)-related adverse events of grade 3 or higher were reported in 31% of patients treated with pembrolizumab and 4% of those who underwent observation. One pembrolizumab-treated patient experienced treatment-related grade 5 pneumonitis.
Disclosure: For full disclosures of the study authors, visit cslide.ctimeetingtech.com.
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