Extramammary Paget's disease treated with of anti-programmed cell death protein 1 therapy after docetaxel therapy failure

Extramammary Paget's disease (EMPD) is a rare skin cancer with no standard treatment for advanced-stage disease. Although docetaxel-based chemotherapy is common, no standard treatment exists. Pembrolizumab is approved for solid tumors with a high tumor mutation burden (TMB) and/or high microsatellite instability, and nivolumab was approved in Japan in February 2024 for unresectable advanced or recurrent epithelial skin malignancies. However, there is a lack of real-world data regarding the efficacy of anti-programmed cell death protein 1 (PD-1) therapy for EMPD. We present the case details of three EMPD patients treated with anti-PD-1 therapy after docetaxel treatment, with TMB values of 17.8, 14.3, and 5.0 mut/Mb, respectively, and we review similar reported cases. Even in the cases with a high TMB, the response to anti-PD-1 therapy was not sufficient. Most cases involve second-line or later treatments, so further research is needed to determine the precise effectiveness of anti-PD-1 therapy as a first-line treatment.