Tumor regression of recurrent chemo-resistant placental site trophoblastic tumor after anti-PD-1 immune checkpoint inhibitor therapy

A placental site trophoblastic tumor (PSTT), characterized by mononuclear and multinuclear extravillous trophoblasts that penetrate the uterus and its vessels, is a rare gestational trophoblastic neoplasia. Due to its rarity, the prognostic factors and ideal treatment are unclear. Recurrent PSTT is thought to be resistant to chemotherapy, but monoclonal antibodies, such as the anti-programmed cell death protein 1 (PD-1) agent pembrolizumab, have recently been reported to be clinically effective for several cancers. We present a recurrent and chemo-resistant PSTT case exhibiting complete response after administration of pembrolizumab. This case suggests a new approach for the management of drug-resistant PSTT. Comaprison between placental site trophoblastic tumor and 6-week gestational whole villus tissues. There is no biological replicate for each conditions.