In a groundbreaking phase 1b clinical trial, researchers have unveiled that the combination of pembrolizumab (Keytruda) and cisplatin-based chemotherapy offers a safe and potentially effective treatment for patients suffering from small cell bladder cancer and small cell/neuroendocrine prostate cancer. The findings, published in Cell Reports Medicine, indicate that this innovative approach could signify a major breakthrough in the treatment of these difficult-to-treat, rare malignancies.

Dr. Arnold I. Chin, MD, PhD, a professor of urology at the David Geffen School of Medicine at UCLA and senior author of the study, expressed optimism about the results. “The combination of pembrolizumab and chemotherapy presents a promising new treatment approach for these challenging-to-treat, rare cancers and could be a significant breakthrough for patient care,” he stated.

The trial enrolled 15 adult participants, of whom 7 had advanced or metastatic small cell bladder cancer and 8 were diagnosed with primary small cell or neuroendocrine prostate cancer. The overall response rate (ORR) across all patients was reported at 43%. Furthermore, progression-free survival (PFS) at 12 months reached an impressive 64%, with variations between the two cohorts — 86% for the bladder cancer group compared to only 43% for the prostate cancer group.

Across both cohorts, overall survival (OS) at 12 months was also encouraging, standing at 79%. Specifically, the OS for the bladder cancer subgroup was 86%, while it was 71% for the prostate cancer cohort. At 24-month follow-up, overall OS remained at 71%, with further disparity observed between the two groups.

One of the key findings has been the correlation between a diverse T cell repertoire and improved progression-free survival, highlighting the potential immune benefits of this therapy. However, while cohort 1 displayed more favorable outcomes, researchers acknowledged that differences in cancer staging may influence the results. Most notably, the bladder cancer cohort consisted mainly of patients with AJCC stage III disease, whereas all prostate cancer patients were stage IV.

On the safety front, treatment-related adverse events (TRAEs) of grade 3 or higher were observed in 40% of participants, with common side effects including fatigue, rash, diarrhea, and peripheral neuropathy. Thankfully, no grade 5 events were documented, nor did any patient need to discontinue treatment due to toxicity.

The authors of the study stress the necessity for larger clinical trials to validate these promising findings and further explore the therapeutic potential of this combination treatment. This research represents a beacon of hope for patients facing these aggressive and often lethal forms of cancer, with the possibility of substantially improved survival outcomes.

As the scientific community eagerly anticipates further replication of these results, the nearness of a new era in cancer treatment looms large for those struggling with small cell bladder and prostate cancers.