SUMMARY: The American Cancer Society estimates that in the United States for 2024, about 83,190 new cases of bladder cancer were diagnosed and approximately 16,840 patients died of the disease. Bladder cancer is the fourth most common cancer in men, but it is less common in women. Bladder cancer accounts for 90% of urothelial cancers, and urothelial cancer can also be found in the renal pelvis, ureter and urethra.
A third of the patients initially present with locally invasive disease. The standard treatment for Cisplatin-eligible patients with Muscle-Invasive Bladder Cancer (MIBC) is neoadjuvant chemotherapy followed by radical cystectomy. However, the high relapse rate and risk of death despite this treatment has prompted further research into optimizing outcomes. There is presently no clear consensus with regards to the routine use of adjuvant Cisplatin-based chemotherapy. Further, not all patients are eligible for adjuvant or neoadjuvant Cisplatin-based chemotherapy.
Immune checkpoints are cell surface inhibitory proteins/receptors that are expressed on activated T cells. They harness the immune system and prevent uncontrolled immune reactions. By inhibiting checkpoint proteins and their ligands, T cells are unleashed, resulting in T cell proliferation, activation and a therapeutic response. It has been noted that PD-L1 is widely expressed in tumor and immune cells of patients with urothelial carcinoma. This in turn helps cancer cells to evade detection from the immune system by binding to the PD-1 receptor on cytotoxic T lymphocytes.
Pembrolizumab (KEYTRUDA®) is a fully humanized, Immunoglobulin G4, anti-PD-1, monoclonal antibody, that binds to the PD-1 receptor and blocks its interaction with ligands PD-L1 and PD-L2. By doing so, it unleashes the tumor-specific effector T cells, and is thereby able to undo PD-1 pathway-mediated inhibition of the immune response.
AMBASSADOR trial (Alliance A031501) is a randomized Phase 3 study, conducted to evaluate whether Pembrolizumab could enhance Disease-Free Survival (DFS) and Overall Survival (OS) in patients with high-risk Muscle Invasive Urothelial Carcinoma (MIUC) after radical surgery, compared to observation alone. This study enrolled 702 patients with high-risk MIUC who underwent radical surgery (cystectomy or nephroureterectomy) within 4-16 weeks before registration. Patients were considered to have high-risk MIUC if they were not eligible for or declined neoadjuvant cisplatin-based chemotherapy and had pT3 or higher, or pN+, or microscopic positive surgical margins, or if they have persistent muscle-invasive disease (defined as a pathological stage of ypT2 or higher or ypN+ or microscopic positive surgical margins) despite the receipt of neoadjuvant chemotherapy at the time of radical surgery. Patients were randomized in a 1:1 ratio, to receive Pembrolizumab 200 mg IV every 3 weeks for 1 year (N=354) or to undergo observation (N=348). Both treatment groups were well balanced and stratification factors for randomization included PD-L1 status (positive or negative, with positivity defined as a Combined Positive Score of 10 or more using the PD-L1 IHC 22C3 pharmDx assay), prior receipt of neoadjuvant chemotherapy, and pathological stage. The median age was 69 years and patients with upper tract and urethral urothelial carcinoma were included in this study. The coPrimary endpoints were DFS and OS, and key Secondary endpoints included DFS and OS stratified by PD-L1 expression.
As of July 2024, with a median follow-up of 44.8 months, the median DFS was significantly longer in the Pembrolizumab group (29.6 months) compared to the observation group (14.2 months). The Hazard Ratio (HR) for disease progression or death was 0.73 (P=0.003), demonstrating a clear benefit. The DFS benefit was observed across all subgroups, regardless of age, PD-L1 status, receipt of neoadjuvant chemotherapy, pathological stage, or tumor location. PD-L1 status therefore should not be used to select patients for treatment with adjuvant Pembrolizumab. The Overall Survival data remain immature. The safety profile of Pembrolizumab was consistent with previous studies, though Grade 3 or higher adverse events were more frequent in the Pembrolizumab group (50.6%) compared to the observation group (31.6%).
In conclusion, adjuvant Pembrolizumab significantly improves DFS in patients with high-risk MIUC post-radical surgery, offering a promising treatment option for this population. These results, together with emerging tools such as circulating tumor DNA (ctDNA) may enable more precise patient selection and stratification, optimizing the use of adjuvant therapies. As Overall Survival data mature and biomarker research evolves, the role of Pembrolizumab may become even more defined within the broader context of urothelial carcinoma treatment.
Adjuvant Pembrolizumab versus Observation in Muscle-Invasive Urothelial Carcinoma. Apolo AB, Ballman KV, Sonpavde G, et al. N Engl J Med 2025;392:45-55
