Partial Response and Stable Disease Correlate with Positive Outcomes in Atezolizumab-treated Patients with Advanced Urinary Tract Carcinoma

The value of a complete response to immune checkpoint inhibitor treatment for urothelial cancer is well recognised, but less is known about long-term outcomes in patients with a partial response or the benefit of achieving disease stabilisation. To determine clinical outcomes in patients with a partial response or stable disease on atezolizumab therapy for advanced urinary tract carcinoma (UTC). Data were extracted from three prospective trials (IMvigor210 cohort 2, SAUL, and IMvigor211) evaluating single-agent atezolizumab therapy for platinum-pretreated advanced UTC. The analysis population included 604 atezolizumab-treated and 208 chemotherapy-treated patients (229 achieving a partial response and 583 achieving stable disease). Atezolizumab 1200 mg every 3 wk until progression or unacceptable toxicity or single-agent chemotherapy for patients in the control arm of IMvigor211. Baseline characteristics, treatment exposure, overall survival, duration of disease control. Partial response and stable disease populations were analysed separately. The population of patients with a partial response included more patients with programmed cell death ligand 1 (PD-L1) expression on ≥5% of tumour-infiltrating immune cells than the stable disease population. The median time to best response was 2.1 mo across trials and treatments, regardless of the type of response. Atezolizumab-treated patients with a partial response had sustained disease control (median overall survival not reached); durations of disease control and overall survival were longer with atezolizumab than with chemotherapy. In patients with stable disease, median overall survival was numerically longer with atezolizumab (exceeding 1 yr) than with chemotherapy. Irrespective of treatment, durations of disease control and survival were shorter in patients with stable disease than in those achieving a partial response. These analyses are limited by their post hoc exploratory nature and relatively short follow-up. Stable disease and partial response are meaningful clinical outcomes in atezolizumab-treated patients with advanced UTC. In this report, we looked at the outcomes in patients whose tumours responded to treatment to some extent, but the tumour did not disappear completely. We aimed to understand whether a modest response to treatment was associated with meaningful long-term outcomes for patients. We found that on average, life expectancy was >1 yr in patients whose disease was stabilised and even lo