A post hoc analysis of the IMvigor130 trial examined overall survival (OS) outcomes by response during first-line induction atezolizumab or placebo plus platinum-based chemotherapy induction for patients with metastatic urothelial carcinoma (mUC).
Results of the analysis are being presented at the American Society of Clinical Oncology 2023 Annual Meeting.
The international, randomized, phase 3 IMvigor130 study evaluated atezolizumab plus platinum-based chemotherapy (Arm A) versus atezolizumab monotherapy (Arm B) and placebo plus platinum-based chemotherapy (Arm C) in patients with mUC. The previously reported final analysis showed that improved OS in Arm A versus Arm C in the intention-to-treat population did not reach statistical significance.
In the initial study, investigators prespecified whether patients received gemcitabine plus cisplatin or gemcitabine plus carboplatin, and this information was used as a randomization stratification factor. Patients without progressive disease were allowed to continue atezolizumab or placebo after 4 to 6 cycles of gemcitabine plus platinum-based chemotherapy.
Enrique Grande, MD, PhD, MSc, and colleagues conducted a post hoc analysis that evaluated postinduction (week 18) OS in patients who completed 4 to 6 cycles of chemotherapy followed by at least 1 dose of atezolizumab or placebo and who had a best response of at least stable disease without progressive disease at any time—up to and including the week 18 tumor assessment.
The time from last patient randomization to the data cutoff (August 31, 2022) was 49 months. Researchers found that OS improvements favoring Arm A over Arm C were greater for patients treated with cisplatin rather than carboplatin. They noted that in the cisplatin subgroup, OS rates at 36 months were 47% and 34% for Arms A and C, respectively, for patients who achieved at least stable disease during induction.
“In this post hoc analysis, the initial response to induction therapy did not seem to impact OS outcomes,” authors of the study concluded. “Consistent with prior analyses, these data suggest that cisplatin-treated patients may derive a greater benefit from the addition of atezolizumab than carboplatin-treated patients.”