Birth weight and subsequent risk of cancer

Background: We aimed to determine the association between self-reported birth weight and incident cancer in the Women's Health Initiative Observational Study cohort, a large multiethnic cohort of postmenopausal women. Methods: 65,850 women reported their birth weight by category (<6. lbs, 6-7. lbs 15. oz, 8-9. lbs 15. oz, and ≥10. lbs). All self-reported, incident cancers were adjudicated by study staff. We used Cox proportional hazards regression to estimate crude and adjusted hazard ratios (aHR) for associations between birth weight and: (1) all cancer sites combined, (2) gynecologic cancers, and (3) several site-specific cancer sites. Results: After adjustments, birth weight was positively associated with the risk of lung cancer (. p=. 0.01), and colon cancer (. p=. 0.04). An inverse trend was observed between birth weight and risk for leukemia (. p=. 0.04). A significant trend was not observed with breast cancer risk (. p=. 0.67); however, women born weighing ≥10. lbs were less likely to develop breast cancer compared to women born between 6. lbs-7. lbs 15. oz (aHR 0.77, 95% CI 0.63, 0.94). Conclusion: Birth weight category appears to be significantly associated with the risk of any postmenopausal incident cancer, though the direction of the association varies by cancer type.