Trial results for the combination of pembrolizumab with chemotherapy in treating participants with locally advanced or metastatic small cell/neuroendocrine cancers of the urothelium or prostate were posted on ClinicalTrials.gov on 2025-06-10. The study reported a 100 percentage of participants achieving a durable response rate in the cohort with metastatic or locally advanced naive small cell bladder cancer.
Background
Pembrolizumab (Keytruda) is a monoclonal antibody. This trial investigated its use alongside combination chemotherapy, including etoposide, docetaxel, cisplatin, and carboplatin, for advanced small cell/neuroendocrine cancers affecting the urothelium or prostate.
Trial design
The study, NCT03582475, was a Phase 1 trial with an enrollment of 15 participants. It investigated the combination therapy in individuals with Bladder Small Cell Neuroendocrine Carcinoma, Castration-Resistant Prostate Carcinoma, Metastatic Bladder Urothelial Carcinoma, Metastatic Urethral Urothelial Carcinoma, and Prostate Carcinoma Metastatic in the Bone.
Key results
Key measurements from the trial included Durable Response Rate (DRR), Overall Response Rate (ORR), Duration of Response (DOR), Progression Free Survival (PFS), and Overall Survival (OS).
- For Durable Response Rate (DRR):
- Cohort 1 (Metastatic or Locally Advanced Naive Small Cell Bladder Cancer) showed a DRR of 100 percentage of participants.
- Cohort 2 (Small Cell or Neuroendocrine Prostate Cancer) showed a DRR of 66.7 percentage of participants.
- For Overall Response Rate (ORR) Per RECIST 1.1:
- Cohort 1 had an ORR of 0.43 proportion of participents.
- Cohort 2 had an ORR of 0.43 proportion of participents.
- For Duration of Response (DOR) Per RECIST 1.1:
- Cohort 2 had a median DOR of 12.6 Months.
- For Proportion of Participants With Progression Free Survival at 12 and 24 Months:
- Cohort 1 at 12 months: 0.86 Proportion of patients.
- Cohort 2 at 12 months: 0.43 Proportion of patients.
- Cohort 1 at 24 months: 0.86 Proportion of patients.
- Cohort 2 at 24 months: 0.14 Proportion of patients.
- For Proportion of Participants With Overall Survival of Cohort 1 and 2 at 12 and 24 Months:
- Cohort 1: 0.86 Proportion of patients.
- Cohort 2: 0.71 Proportion of patients.
What this means
The results from this Phase 1 trial suggest promising activity for pembrolizumab in combination with chemotherapy for these aggressive small cell/neuroendocrine cancers. The particularly high durable response rate observed in the small cell bladder cancer cohort, alongside notable overall response rates and survival proportions in both cohorts, warrants further investigation. While the trial involved a small number of participants, these initial findings provide important data for future research into these difficult-to-treat malignancies.
Source
The information regarding these trial results was obtained from ClinicalTrials.gov, a public database of clinical studies. The results for study NCT03582475, titled "Pembrolizumab With Combination Chemotherapy in Treating Participants With Locally Advanced or Metastatic Small Cell/Neuroendocrine Cancers of Urothelium or Prostate," were posted on 2025-06-10 on clinicaltrials.gov.