Background: In the phase 3 CASPIAN study (NCT03043872), first-line durvalumab plus etoposide and cisplatin or carboplatin (EP) significantly improved OS versus EP alone in patients with extensive-stage (ES)-SCLC (HR 0.73 [95% CI 0.59–0.91; p = 0.0047]). Here we report results for a preplanned subgroup analysis of patients recruited in Japan. Methods: Treatment-naïve patients with ES-SCLC received either 4 cycles of durvalumab 1500 mg plus EP q3w followed by maintenance durvalumab 1500 mg q4w until disease progression or up to 6 cycles of EP q3w. The primary endpoint was OS. Secondary endpoints included progression-free survival (PFS), objective response rate (ORR), safety, and tolerability. Results: In the Japan subgroup, 18 patients were randomized to durvalumab plus EP and 16 patients to EP. At the interim analysis with a median follow-up of 12.5 months in the subgroup, OS numerically favored durvalumab plus EP versus EP (HR 0.77 [95% CI 0.26‒2.26]; median not reached vs 15.2 months). PFS was similar for durvalumab plus EP versus EP (HR 0.90 [95% CI 0.43‒1.89]). Confirmed ORR was 89% with durvalumab plus EP versus 69% with EP. Adverse events (AEs) of CTCAE grade 3 or 4 were reported in 78% versus 94% of patients in the durvalumab plus EP versus EP arms. There were no AEs leading to treatment discontinuation or death in the Japan subgroup. Conclusion: First-line durvalumab plus EP was effective and well tolerated in Japanese patients with ES-SCLC. Despite the small size of the Japan subgroup, results were generally consistent with the global study population.
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