An essential feature of cancer is its ability to evade the immune system. Multiple mechanisms are used for this purpose, including the disruption of antigen presentation and suppression of the immune response. The latter mechanism involves the activation of T-cell inhibition by recruiting regulatory T cells that weaken this response. Recent progress in understanding the ability of cancer to evade the immune system has paved the way to develop strategies to reverse this process and reactivate the immune system. Particularly, immune checkpoint signaling between T cells and tumor cells has been targeted with a new class of drug, immune checkpoint inhibitors. Immunotherapy has been an established and effective treatment in bladder cancer since 1976 when Morales and colleagues demonstrated that intravesical treatments with bacillus Calmette-Guérin can treat carcinoma in situ and prevent nonmuscle invasive urothelial cancer recurrence.1,2 This treatment elicits a cytotoxic response via antigenic presentation by bladder tumor cells.
Cytotoxic T-lymphocyte-associated protein (CTLA)-4, programmed death-1 (PD-1) and programmed death-ligand-1 (PD-L1) are molecules that downregulate the immune response and are targets of therapeutic antibodies that have demonstrated clinical efficacy across a wide range of malignancies. Five such agents—pembrolizumab, atezolizumab, nivolumab, avelumab and durvalumab—were recently approved by the US Food and Drug Administration (FDA) for clinical use in patients with advanced urothelial cancers.3 This class of agents also has been approved for several other malignancies, most notably in melanoma, non-small cell lung cancer, and renal cell carcinoma.3
Immune Biology
CTLA-4 is expressed on activated CD4 and CD8 T cells and competes with CD28 on T cells to interact with the costimulatory B7 proteins on antigen presenting cells. The CD28/B7 interaction promotes T-cell activation and effector functions, and the CTLA-4/B7 interaction inhibits them. In addition, PD-1 is a receptor expressed on CD4 and CD8 T cells, T regulatory (Treg) cells, B cells and natural killer (NK) cells that interacts with its ligand PD-L1 to suppress the immune response. Urothelial cancer possesses features that make it an adequate target for immunotherapeutic agents. Primarily, it is characterized by a high-mutation load, which lends itself to an increased expression of immunogenic antigens on tumor cells.4
Immunotherapy Treatments in Cisplatin-Ineligible Patients
Cisplatin-based chemotherapy is the first-line treatment and standard of care in unresectable or metastatic urothelial cancer. However, many patients are unable to receive cisplatin secondary to renal dysfunction, poor performance status, or other comorbidities. Alternative cytotoxic therapies in the first-line setting such as carboplatin-based regimens are associated with inferior outcomes and poor tolerability. There is, therefore, a need for effective and well-tolerated therapies in cisplatin-ineligible patients (Table).
In the phase 2 Keynote-052 trial, 370 cisplatin-ineligible patients were treated with the anti-PD-1 antibody pembrolizumab 200 mg every 3 weeks for up to 2 years.5At a median follow-up of 9.5 months, the objective response rate (+ORR) was 29% for the entire cohort, with a 7% complete response (CR) rate, and a 22% partial response (PR) rate.5 The median duration of response had not been reached at the time of analysis. Responses were seen regardless of PD-L1 expression, although high response rates were noted in patients whose tumors had PD-L1 expression > 10%. Pembrolizumab had an acceptable tolerability profile in this population. The most common grade 3 or 4 treatment-related adverse event (AE) was fatigue at 2%; 5% of patients discontinued therapy due to treatment related AEs, whereas 17% of patients had immune-mediated AEs.5
Similarly, in a single-arm phase 2 trial, atezolizumab, an anti-PD-L1 antibody, dosed at 1,200 mg every 3 weeks was used as first-line therapy in 119 patients with advanced urothelial cancer who were cisplatin ineligible. At a median follow-up of 17 months, the ORR was 23%, with a 9% CR rate. The median duration of response had not been reached. Median progression free survival (PFS) was 2.7 months, whereas overall survival (OS) was 16 months. Eight percent of patients had an AE leading to treatment discontinuation, and 17% had immune-mediated AEs.6 Both pembrolizumab and atezolizumab were granted FDA approval in 2017 for patients with locally advanced or metastatic urothelial carcinoma who are not eligible for cisplatin-based chemotherapy.3
