Whole-exome sequencing reveals germline-mutated small cell lung cancer subtype with favorable response to DNA repair–targeted therapies

Heritable defects in cancer genes define a subset of small cell lung cancer with distinct therapeutic vulnerabilities. Genetics of small cell lung cancer Small cell lung cancer (SCLC) is generally regarded as a smoker’s cancer. However, the genetic factors that affect susceptibility to SCLC have not been fully evaluated. Tlemsani and colleagues performed whole-exome sequencing on the germ lines of a cohort of participants with SCLC, finding that almost half the cohort carried deleterious variants in cancer-predisposing genes. Those with pathogenic germline variants had better response to platinum-based chemotherapy, and in one patient, the genetic information was used to select a combination of chemotherapeutic agents that resulted in reduction of tumor burden. Germline mutations in SCLC could be used to influence medical management and family member testing. Because tobacco is a potent carcinogen, secondary causes of lung cancer are often diminished in perceived importance. To assess the extent of inherited susceptibility to small cell lung cancer (SCLC), the most lethal type of lung cancer, we sequenced germline exomes of 87 patients (77 SCLC and 10 extrapulmonary small cell) and considered 607 genes, discovering 42 deleterious variants in 35 cancer-predisposition genes among 43.7% of patients. These findings were validated in an independent cohort of 79 patients with SCLC. Loss of heterozygosity was observed in 3 of 14 (21.4%) tumors. Identification of variants influenced medical management and family member testing in nine (10.3%) patients. Unselected patients with SCLC were more likely to carry germline RAD51 paralog D (RAD51D), checkpoint kinase 1 (CHEK1), breast cancer 2 (BRCA2), and mutY DNA glycosylase (MUTYH) pathogenic variants than healthy controls. Germline genotype was significantly associated with the likelihood of a first-degree relative with cancer or lung cancer (odds ratio: 1.82, P = 0.008; and 2.60, P = 0.028), and longer recurrence-free survival after platinum-based chemotherapy (P = 0.002), independent of known prognostic factors. Treatment of a patient with relapsed SCLC and germline pathogenic mutation of BRCA1 interacting protein C-terminal helicase 1 (BRIP1), a homologous recombination–related gene, using agents synthetically lethal with homologous recombination deficiency, resulted in a notable disease response. This work demonstrates that SCLC, currently thought to result almost exclusively from tobacco exposure, may have an inherited predisposition and lays the groundwork for targeted therapies based on the genes involved.