Family History of Cancer and Risks of Concordant and Discordant Cancers: A Nationwide Cohort Study of Korean Women

Evidence on discordant familial cancer associations and their relevance in non‐Western populations remains limited. This study assessed concordant and discordant cancer risks across major cancer sites in Korean women by comparing individuals with and without a family history of cancer. In total, 5,015,485 cancer‐free women aged ≥ 40 years who participated in the national breast cancer screening program were included. Participants reported a family history of stomach, colorectal, liver, breast, cervical, or other cancers at screening. The risks of overall, site‐specific, concordant (same cancer site as the family history), and discordant cancers (different cancer sites from the family history) were evaluated. Overall, a family history of any cancer was associated with a higher hazard of cancer (HR, 1.11; 95% CI, 1.10–1.12), with similar associations for cancers diagnosed before age 50 years (HR, 1.12; 95% CI, 1.09–1.14) and those diagnosed at age 50 years or older (HR, 1.13; 95% CI, 1.12–1.14). Elevated hazards associated with a family history were observed for most cancer sites, except for cervical, kidney, and brain cancers. Concordant associations were observed for gastric, colorectal, breast, and liver cancers (HRs, 1.36–2.43), whereas cervical cancer showed no significant concordant association. Modest but statistically significant discordant associations were observed across the five family history cancer types (HRs, 1.05–1.13). These associations were generally consistent across age groups. A family history of cancer was associated with both overall and site‐specific cancer risk, with stronger associations for concordant cancers and more modest associations for discordant cancers.