ESMO 2025 | STAMP: adjuvant pembrolizumab in resected Merkel cell carcinoma

So the STAMP trial is a study that is a phase three trial that was designed to test the role of immunotherapy in the form of pembrolizumab in patients with Merkel cell carcinoma who have surgically resected tumors. Merkel cell carcinoma is a very rare and aggressive type of neuroendocrine skin cancer and this is actually the largest study in the world to be completed to look at this question. We designed a phase three trial where patients would be randomized to either treatment with pembrolizumab or standard of care. Patients with stage 1b to 3 Merkel cell carcinoma, stage one needed to have had a sentinel lymph node biopsy done, were included in the trial. Patients were permitted to have up to a performance status of two, and radiation therapy was permitted to be delivered to patients in both arms at the physician’s discretion. So the trial enrolled 292 patients. The primary endpoint of the study was relapse-free survival, with a co-primary endpoint of overall survival that will be reported at a future meeting. And what we found is that there’s a numerically but not statistically significant difference between the two arms of 83% alive with that recurrence at 12 months and 71% in the observation arm. And what we did find also is that a secondary endpoint of distant metastasis-free survival with a p-value of 0.032 was noted and hazard ratio of 0.58. And that suggests that even if pembrolizumab was not successful in improving statistically the rate of local recurrences, it did protect against distant spread of disease. And that’s important because distant spread is what is often life-threatening in patients.

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