Purpose

Randomized phase 2, multicenter, biomarker directed clinical trial with a safety lead-in to assess the efficacy of Stenoparib plus Temozolomide (TMZ) in relapsed Small Cell Lung Cancer patients. Participants will receive either a combination of oral Stenoparib at the highest tolerated dose with oral Temozolomide 40mg daily or standard of care Lurbinectedin for 21-day cycles. The Dose limiting toxicity period will be 1 cycle of 21 days. This study will explore if the biomarkers the investigators test predict sensitivity to the combination of Stenoparib plus TMZ and therefore leads to a better treatment response. There are two potential tests of biomarkers that can predict who would benefit from the oral combination of Stenoparib with Temozolomide (TMZ), but they have not been evaluated. This study will test for this sensitivity using a biomarker (found in the blood that may be related to how a person reacts to a drug). The study will include 9 participants for the safety evaluation of the Stenoparib+TMZ group and 5 participants for the standard of care Lurbinectedin safety group. We will first determine safety dose for the experiment arm which, will include 3 groups with 3 participants in each group. Three doses of Stenoparib will be evaluated for toxicity. The initial starting dose of Stenoparib will be 200mg po QD. Once the maximum tolerated dose has been determined, participants will be assigned to one of the two groups in the phase 2 portion. Group 1 will be patients that test negative for the biomarker and will receive treatment with Lurbinectedin as per standard of care guidelines. Group 2 will be patients that test positive for the biomarker that will be randomly assigned to either the combination of Stenoparib plus Temozolomide (TMZ) or Lurbinectedin.