Dr. Alan P. Lyss
A second interim overall survival (OS) analysis suggested that atezolizumab monotherapy provides a clinical benefit as first-line treatment for mUC patients with PD-L1–expressing immune cells representing at least 5% of the tumor area (IC2/3), including patients who are cisplatin ineligible.
The analysis also suggested that atezolizumab plus chemotherapy produces similar OS results as chemotherapy plus placebo, but patients receiving atezolizumab may do better with cisplatin-based chemotherapy than with carboplatin-based chemotherapy.
These results were reported in two presentations at the American Association for Cancer Research Annual Meeting 2021: Week 1.
Current guidelines from the National Comprehensive Cancer Network and the European Society for Medical Oncology recommend atezolizumab monotherapy for cisplatin-ineligible patients with mUC and PD-L1 IC2/3.
The ongoing phase 3 IMvigor130 trial was designed to compare atezolizumab plus gemcitabine/platinum chemotherapy, atezolizumab monotherapy, and placebo plus chemotherapy. Platinum-based chemotherapy included either cisplatin or carboplatin, per investigator choice.
Coprimary endpoints for IMvigor130 were progression-free survival (PFS) and OS for atezolizumab plus chemotherapy versus placebo plus chemotherapy. The hierarchical study design dictated that OS would only be assessed for the comparison of atezolizumab monotherapy versus placebo-chemotherapy in the overall and PD-L1 IC2/3 populations if there was statistical improvement in OS for the atezolizumab-chemotherapy arm over the placebo-chemotherapy arm.
Secondary endpoints were overall response rate (ORR; per RECIST 1.1), duration of response (DOR) for all patients, and PFS for the comparison between atezolizumab monotherapy and placebo-chemotherapy. Exploratory analyses were performed on cisplatin-ineligible patients by PD-L1 status.
At the time of the primary analysis, an OS benefit for atezolizumab-chemotherapy over placebo-chemotherapy was not observed. Therefore, the OS benefit of atezolizumab monotherapy versus placebo-chemotherapy was not assessed. However, a trend toward improved OS was noted with atezolizumab for PD-L1 IC2/3 patients, including cisplatin-ineligible patients.
Atezolizumab vs. placebo-chemo
Ian D. Davis, MBBS, PhD, of Monash University in Melbourne, presented the second interim analysis of OS with atezolizumab monotherapy versus placebo plus chemotherapy (Abstract CT040).
The median follow-up was 14.9 months for atezolizumab monotherapy (n = 360) and 11.8 months for placebo-chemotherapy (n = 359). The median OS was 15.2 months and 13.1 months, respectively (hazard ratio, 0.99; 95% confidence interval, 0.83-1.19). There was no apparent OS benefit of atezolizumab for any clinically selected subgroup.
The ORR was 23.4% for atezolizumab monotherapy and 44.1% for placebo-chemotherapy. The median DOR was more than 3.5 times longer for atezolizumab monotherapy than for placebo-chemotherapy – 29.6 months and 8.1 months, respectively.
Although there was no formal statistical comparison, exploratory subgroup analyses demonstrated that the median OS for the PD-L1 IC2/3 patients appeared higher in the atezolizumab monotherapy arm than in the placebo-chemotherapy arm – 27.5 months and 16.7 months, respectively.
Similarly, the median OS for cisplatin-ineligible PD-L1 IC2/3 patients appeared higher for atezolizumab monotherapy than for placebo-chemotherapy – 18.6 months and 10.0 months, respectively.
In terms of safety, atezolizumab monotherapy compared favorably with placebo plus chemotherapy. There were similar numbers of grade 3/4 adverse events and comparable adverse events leading to discontinuation of treatment in both arms.
The atezolizumab monotherapy arm had fewer adverse events leading to withdrawal from any treatment, when compared with the placebo-chemotherapy arm – 7% and 34%, respectively. Two patients in the atezolizumab arm and one in the placebo-chemotherapy died of treatment-related causes.