Background: Chemotherapy (CT) is a mainstay of cancer treatment; however, its side effects, notably myelosuppression, cause significant suffering. Trilaciclib (T) is an IV CDK4/6 inhibitor that protects hematopoietic stem and progenitor cells by preventing proliferation during CT administration. Results from three randomized, double-blind, placebo (P)-controlled phase II trials in patients (pts) with extensive-stage small cell lung cancer (ES-SCLC) have previously been reported. Data from these studies were pooled to understand the effects of T on specific myelosuppression endpoints with greater statistical precision. Methods: All pts received standard CT (etoposide/carboplatin [E/C], E/C/atezolizumab, or topotecan) plus T or P. Analyses were conducted on pooled intent-to-treat datasets from three ES-SCLC studies (NCT02499770; NCT03041311; NCT02514447). Results: 123 pts were treated with T and 119 with P. Median age in both groups was 64 years. Addition of T decreased measures of myelosuppression and the need for supportive care interventions (Table). From the pooled dataset, median OS and PFS (months [95% CI]) were comparable between pts treated with T vs P (OS: 10.6 [9.1, 11.7] vs 10.6 [7.9, 12.8]; PFS: 5.3 [4.6, 6.1] vs 5.0 [4.4, 5.5], respectively). Fewer pts on T had grade 3/4 hematologic events (54 [44.3%]) vs P (91 [77.1%]). Among pts who continued after cycle 1, 11 pts (9.2%) treated with T had ≥1 CT dose reduction vs 36 (30.8%) with P. Conclusions: T significantly and meaningfully reduced both CT-induced myelosuppression and its consequences, with no detrimental effect on PFS or OS, thus improving the patient experience with CT in ES-SCLC. T has potential to become a new standard of care for preventing myelosuppression in SCLC.

*Two-sided p value calculated using nonparametric ANCOVA; other p values calculated using modified Poisson method.