Biomarker Directed Trial of Temozolomide and Stenoparib in Relapsed SCLC

Inclusion Criteria: * Age 18 years or older at the time of consent. * Histological or cytological diagnosis of extensive-stage small cell lung cancer. * Patients must have received one prior line of systemic therapy. * Patients must have received first-line therapy with Carboplatin and Etoposide. * If patient is re-treated with Carboplatin and Etoposide at least 6 months or more after first regimen, this will still be considered one line of * treatment and they will qualify for this trial. * Patients could have received immunotherapy in combination with the chemotherapy regimen. * Patients who have received Tarlatamab as second line treatment are allowed. * ECOG Performance status 0-2. * Measurable disease as per RECIST v1.1 (NOTE: Previously irradiated lesions are eligible as a target lesion only if there is documented progression of the lesion after irradiation). * Adequate bone marrow, liver, and renal function, as assessed by the following laboratory requirements: * ANC 1.5 * Platelets 100 × 109/L * Hemoglobin 9 g/dL or 5.6 mmol/L * Aspartate transaminase and alanine transaminase 2.5 × upper limit of normal (ULN), \<5× in patients with known liver metastases * Serum total bilirubin 1.5 × ULN, 1.5-3.0 × ULN may be included appropriate starting dose adjustment to 200 mg daily. * Creatinine \<1.5 × ULN or estimated glomerular filtration rate (GFR) 50 ml/min by Cockcroft-Gault. Depending on scenario, GFR 30-49 can be --permissible. * Women of child-bearing potential must not be pregnant or breastfeeding and must have a negative pregnancy test within 72 hours of cycle 1 Day 1. * Male and female subjects of child-bearing potential must agree to use a double-barrier method of birth control from the screening visit through 180 days after the last dose of study drug. * Male subjects of child-bearing potential must agree to use a double-barrier method of birth control including use a male condom (and should also be advised of the benefit for a female partner to use a highly effective method of contraception as a condom may break or leak) and must agree to refrain from donating sperm from screening visit through at least 90 days after the last dose of study drug. * Previously treated or asymptomatic brain metastases are allowed. Exclusion Criteria: * Unstable or clinically significant concurrent medical condition, psychiatric illness or social situation that would, in the opinion of the investigator, jeopardize the safety of a subject and/or their compliance with the protocol. * Clinically significant acute infection requiring systemic antibacterial, antifungal, or antiviral therapy. (Suppressive therapy for chronic infections allowed, for example: Subjects with HIV/AIDS with adequate antiviral therapy to control viral load would be allowed. Subjects with viral hepatitis with controlled viral load would be allowed while on suppressive antiviral therapy.) * Prior exposure to lurbinectedin, TMZ or stenoparib. * Pregnant or breastfeeding. * Clinical significant cardiovascular disease (ie active) * Subject with known hypersensitivity to Stenoparib components * Subject with known history of myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML) are excluded. * Subject with QTc interval 470 for females, or 450 for males per electrocardiogram (EKG) at screening.