1742PDTrilaciclib (T) decreases myelosuppression in extensive-stage small cell lung cancer (ES-SCLC) patients receiving first-line chemotherapy plus atezolizumab

Abstract Background Chemotherapy (chemo)-induced damage of hematopoietic stem and progenitor cells (HSPC) causes multi-lineage myelosuppression. Current supportive therapies are lineage specific and administered after damage has occurred. T, a highly selective, reversible CDK4/6 inhibitor and first-in-class myelopreservation agent, preserves HSPCs during chemotherapy, improving its safety and tolerability. This trial (NCT03041311) studied the benefits of T in ES-SCLC patients receiving 1L chemo + atezolizumab (A). Methods This placebo (P)-controlled, double-blind, Ph2 study randomized (1:1) chemo-naïve ES-SCLC pts with adequate organ function, ECOG 0-2, and no symptomatic brain mets, to T or P with etoposide/carboplatin/A (ECA) for four induction cycles followed by maintenance (A). Prophylactic growth factors were prohibited in cycle 1; otherwise standard supportive care was allowed. Prespecified lineage-specific endpoints assessed the effect of T on myelosuppression. Tumor response was assessed using RECIST v1.1. FACT-L and FACT-An were evaluated. Results T + ECA was well tolerated with fewer ≥ G3 AEs in T (62% overall; 50% any drug related) vs P (87%; 74%), primarily due to less heme toxicity. T improved ANC, RBC measures and SOC interventions (Table). T also delayed time to deterioration in some PRO functioning domains and anemia symptoms. T did not affect chemo efficacy as measured by ORR and PFS; OS will be presented. Table: 1742PDParameter, n [1]ECA + P N = 53ECA + T N = 54Adjusted 1-sided P- valueMean Duration (d) G4 ANC in Cycle 1[2]40