We found that while DDR mutations and HR deficiency (HRD) scores were not predictive in SCLC, expression levels of several markers including SLFN11, ATM, and E-cadherin (reflecting epithelial-to- mesenchymal transition (EMT) status) determined response to both PARP inhibitors and several classes of chemotherapy in preclinical models. The gene discussed is ATM; the disease is small cell lung carcinoma.