Lung cancer is by far the leading cause of cancer death among both men and women worldwide and the second most common cancer in terms of new cases. Small cell lung cancer (SCLC) is the deadliest form of lung cancer. The standard first-line treatment is the combination of carboplatin, etoposide, and atezolizumab. While response rates for this regimen are high (roughly 60%), the duration of response is short, typically 4 months. Following progression after the 1st line treatment of SCLC, there is no consensus regarding subsequent therapy. Lurbinectedin is FDA approved and is increasingly preferred in clinical practice. Toxicity was significant, but appeared favorable compared to historic results with topotecan, leading to the adoption of this therapy for second-line SCLC. The toxicity profile was dominated by myelosuppression. This study investigates the effect of Trilaciclib on myelosuppression rate in subjects with platinum refractory extensive stage (ES)- SCLC receiving Lurbinectedin as well as the clinical synergy of Trilaciclib and Lurbinectedin combination.