The study examines the gene-gene interactions between two DNA base excision repair genes on lung cancer risk: the ADPRT (adenosine diphosphate ribosyltransferase) Val762Ala polymorphism and the XRCC1 (X-ray repair cross-complementing group 1) Arg366Gln polymorphism (both having three genotypes). The gene discussed is PARP1; the disease is lung cancer.