Genetic polymorphism in the manganese superoxide dismutase gene, antioxidant intake, and breast cancer risk: results from the Shanghai Breast Cancer Study

Population-based case-control study in urban Shanghai conducted 1996–1998; female participants aged 25–64; 1459 breast cancer cases and 1556 age-frequency-matched controls; MnSOD Val-9Ala genotyped (via PCR-RFLP); data collected on demographics, menstrual/reproductive history, lifestyle, and dietary antioxidant intake; pathology-confirmed cases.

Ala/Ala genotype associated with a non-significant 1.3-fold increase in breast cancer risk vs Val/Val (OR 1.3, 95% CI 0.7–2.3). In premenopausal women, risk increased (OR 1.8, 95% CI 0.9–3.7). Among premenopausal women with higher BMI or longer menstruation, ORs were about 2.5 (0.9–7.0) and 2.6 (0.8–8.0). The association tended to be stronger among premenopausal women with low intake of fruits/vegetables, selenium, or antioxidant vitamins, though not statistically significant. Conclusion: MnSOD Ala/Ala may be linked to a modest, non-significant increase in breast cancer risk in Chinese women with higher oxidative stress or lower antioxidant intake; low Ala allele frequency and lack of statistical significance limit conclusions; larger studies are needed to confirm.

Low Ala allele frequency (~14%) limiting statistical power; small numbers in stratified subgroups reduce precision; most associations not statistically significant; observational design; may not generalize beyond Chinese population.