The phase 2 SWOG S1512 trial ( NCT02775851 ) was designed to evaluate the response to pembrolizumab (anti-PD-1) in individuals with desmoplastic melanoma. Here we report the results of cohort A of the trial, evaluating the pathological complete response (pCR) rate of neoadjuvant PD-1 blockade in surgically resectable desmoplastic melanoma. Secondary endpoints included clinical response rate, overall survival and toxicities. Twenty-eight eligible individuals with resectable desmoplastic melanoma received intravenous pembrolizumab (200 mg) every 3 weeks three times, followed by excision. Tissue samples before treatment, at 3-5 weeks after treatment initiation and at the time of surgery were reviewed. The primary endpoint of pCR rate by local pathological review was 71% (95% confidence interval, 51-87%; P < 0.001), which met the prespecified endpoint. There were two (7%) grade 3 treatment-related adverse events. At three years of follow-up, four participants have died, none known to be from melanoma or adverse events. In conclusion, neoadjuvant pembrolizumab in individuals with resectable desmoplastic melanoma results in a high pCR rate with acceptable safety profile. Clinicaltrials.gov: NCT02775851 .
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