The randomized, phase 2 study evaluated atezolizumab as maintenance therapy following concurrent chemoradiotherapy (CRT) in patients with limited-stage small cell lung cancer (LS-SCLC). Patients with performance status 0 to 2 and no progression after platinum/etoposide chemotherapy and concurrent thoracic radiotherapy of 45 Gy in 30 fractions or 60 Gy in 40 fractions were randomized 1:1 to receive atezolizumab 1200 mg every 3 weeks for 1 year or observation only. Atezolizumab was initiated 3 to 7 weeks after CRT treatment. The primary endpoint was overall survival (OS), with secondary endpoints including progression-free survival (PFS), overall response rate (ORR), and toxicity.
A total of 216 patients were enrolled across 37 European hospitals, with 170 randomized equally between the atezolizumab and observation arms. The median age of the patients was 66 years. In addition, 83.5% of patients in the atezolizumab group and 81.2% of patients in the observation group had stage III disease. The ORR to CRT was high in both groups (atezolizumab, 95%; observation, 94%), with 67% of patients in each arm receiving prophylactic cranial irradiation. After a follow-up of 45.1 months (95% confidence interval [CI], 40.7-47.3 months), the atezolizumab arm did not demonstrate significant improvement in OS (median OS, 43.4 vs 38.8 months; hazard ratio [HR], 1.14; 95% CI, 0.76-1.71) or PFS (median PFS, 21.1 vs 15.9 months; HR, 0.89; 95% CI, 0.61-1.30) compared with the observation arm.
Grade 3 to 4 toxicities occurred more frequently in the atezolizumab arm (34.1%) than in the observation arm (20.0%). Notable events in the atezolizumab group included dyspnea (n=8) and fatigue (n=7), and endocrinopathies (n=5), whereas notable events in the chemotherapy group included anorexia (n=6), neuropathy (n=5), and dyspnea (n=4). Three treatment-related deaths resulting from neurotoxicity, pneumonitis, and pneumonia were reported in the atezolizumab group.
The study concluded that atezolizumab maintenance therapy after CRT did not improve survival outcomes in LS-SCLC and was associated with higher toxicity. This indicates that the benefit of atezolizumab after CRT may be minimal, and additional research is needed for other potential treatment options for this patient population.
Source: Gronberg B, et al. Randomized phase II trial investigating whether atezolizumab after chemoradiotherapy (CRT) prolongs survival in limited stage (LS) small cell lung cancer (SCLC). Presented at: 2025 ASCO Annual Meeting. May 30-June 3, 2025; Chicago, IL. Abstract LBA8005.