An International Study of Pembrolizumab for Drug-Resistant Gestational Trophoblastic Neoplasia

Data to guide use of anti-PD1 immunotherapy with pembrolizumab for gestational trophoblastic neoplasia (GTN) that is chemotherapy-resistant or in adjuvant settings are limited. We conducted an international retrospective study of pembrolizumab in GTN, including patients with ultra-high-risk choriocarcinoma and poor-prognosis placental site and epithelioid trophoblastic tumors (PSTT/ETT), with up to 8 years of follow-up.

We collected data on patients with GTN cases who received treatment with pembrolizumab between May 2015 and June 2023 from 20 centers in 16 countries. Cases were identified at Charing Cross Hospital, London; international centers with expertise in GTN were directly invited to identify and submit eligible cases treated during the study period. Clinical data were gathered from medical records using a standardized case-report form, curated centrally. Twenty-three samples were characterized by multiplex immunofluorescence, shallow whole-genome, and whole-transcriptome sequencing.

We identified 76 patients with drug-resistant GTN treated with pembrolizumab. This included 60 (78.9%) patients with GTN and measurable disease. Complete response was achieved in 71.7% (n=43 of 60; 95% confidence interval [CI], 60.3 to 83.1). Two-year overall survival (OS) was 85.6% (95% CI, 76.7 to 95.4), with median follow-up from pembrolizumab initiation of 25.4 months (range, 1.4 to 95.7). Sixteen (21.1%) received adjuvant pembrolizumab instead of high-dose chemotherapy, of whom 15 had poor-prognosis PSTT/ETT. No deaths were observed with median follow-up of 33.1 months (range, 7.7 to 68.6) from first remission. There were no identified grade 4 or worse immune-related toxicities. On multiplex immunofluorescence, the median fluorescence intensity between-group difference in cancer cell HLA-G expression (responders minus nonresponders) was 0.6 (95% CI, 0.3 to 1.0). Shallow whole-genome and whole-transcriptome sequencing suggested low HLA-G expression could be due to transcriptional control.

In this retrospective study without a control group, pembrolizumab was associated with durable responses in multidrug-resistant GTN and showed potential activity as adjuvant therapy for poor-prognosis PSTT/ETT. HLA-G expression warrants further exploration as a response biomarker. (Funded by Imperial College Experimental Cancer Medicine Centre and others.).