EORTC 1417 - REACTION: A phase II study of etoposide and cis/carboplatin with or without pembrolizumab in untreated extensive small cell lung cancer

Background Anti-PD-L1 antibodies with platinum-etoposide extend overall survival (OS) of extensive disease Small Cell Lung Cancer (ED-SCLC) patients. We evaluated the benefit of first-line pembrolizumab with platinum-etoposide in chemo-sensitive ED-SCLC. Methods REACTION is a multicenter, open-label, randomized phase II trial. Eligible patients (responders after 2 cycles of platinum-etoposide) were randomized 1:1 to experimental arm pembrolizumab in combination with 4 cycles of platinum-etoposide then pembrolizumab vs platinum-etoposide in the control arm. The primary endpoint was progression free survival (PFS). Circulating tumour cells (CTCs) were enumerated and their association with PFS and OS was investigated. Results Between Feb 7, 2018 and Oct 31, 2019, 125 patients were recruited (61 vs 64 experimental and control arms respectively) with 119 (58 vs 61) eligible and receiving at least one dose of treatment. Baseline characteristics were median age 65 vs 63.5 years, PS 1 (62 vs 60 %), and brain metastases (8 vs 11 %), in the experimental and control arms respectively. Amongst 124 patients who started treatment, 46 (37 %) experienced adverse events grade ≥ 3 for pembrolizumab arm vs 26 % in the control arm. Response rate was 61 % (67 vs 56 %). Median PFS (95 % CI) was 4.7 months (4.2, 5.6) vs 5.4 (4.7, 5.6), HR (80 % CI) = 0.84 (0.65, 1.09) and 1-sided p = 0.194. Median OS (95 % CI) was 12.3 months (8.9, 14.8) vs 10.4 (8.2, 12.2), HR (80 % CI) = 0.73 (0.54, 1.0) and 1-sided p = 0.097. CTC count per 7.5 ml blood at randomization was associated significantly with both PFS and OS regardless of treatment arms. Conclusions Pembrolizumab added to platinum-etoposide did not improve PFS over platinum-etoposide alone in chemo-sensitive patients with ED.