BACKGROUND

Beneficial effects of cruciferous vegetable intake on breast cancer survival have long been postulated because they are primary sources of isothiocyanates, phytochemicals with multifaceted anticancer activities. However, observational studies have reported inconsistent results. We hypothesized that variations in vegetable types and polymorphisms in isothiocyanate-metabolizing genes across self-identified race and ethnicity contribute to such inconsistencies.

METHODS

In the Pathways Study, a prospective cohort study of women diagnosed with breast cancer between 2005 and 2013 at Kaiser Permanente Northern California, cruciferous vegetable intake was assessed at diagnosis using food frequency questionnaires. Functional polymorphisms in isothiocyanate-metabolizing genes were identified in the literature and genotyped. Cox proportional hazards models were used to calculate hazard ratios (HR) and 95% confidence intervals (CI). The analysis included 3,656 (2,489 non-Hispanic White, 241 Black, 463 Asian, 378 Hispanic, and 85 others) participants.

RESULTS

An overall inverse association between cruciferous vegetable intake and risk of total invasive events, including recurrence, second primary cancers, and death, was observed in age-adjusted models (HR, 0.86; 95% CI per serving, 0.77-0.97), whereas no significant dose-dependent associations were observed in multivariable analyses (HR, 0.91; 95% CI per serving, 0.78-1.05). Within racial and ethnic groups, significant associations were observed with different individual vegetables and in women with certain genotypes of isothiocyanate-metabolizing genes.

CONCLUSIONS

Vegetable types and isothiocyanate-metabolizing gene polymorphisms affect the associations of cruciferous vegetable intake with breast cancer survival.

IMPACT

Our findings highlight the importance of considering race and ethnicity when evaluating cruciferous vegetable intake in breast cancer survival.