Soy intake after breast cancer diagnosis reduces recurrence risk in most studies
Most prospective cohort studies evaluating the association between dietary soy intake after breast cancer diagnosis found an overall 21% decrease in recurrence with high soy intake and a 15% reduction in mortality (TABLE1-6).
Investigators in a meta-analysis of 5 studies that followed women for 4 to 7 years after first breast cancer diagnosis found that higher soy intake was associated with lower mortality but not less recurrence in women who were estrogen receptor positive. Both recurrence and mortality were decreased in estrogen receptor negative women.6
The study also found lower recurrence and mortality in premenopausal women with higher soy intake (recurrence hazard ratio [HR]=0.91; 95% CI, 0.72-1.14; mortality HR=0.78; 95% CI, 0.69-0.88). In postmenopausal women, higher intake was likewise associated with improvement of both outcomes (recurrence HR=0.67; 95% CI, 0.56-0.80; mortality HR=0.81; 95% CI, 0.73-0.91).
An earlier meta-analysis of 4 prospective cohort studies, 2 of which were not included above, also found reduced risk of breast cancer recurrence in groups with high vs low soy isoflavone intake (HR=0.84; 95% CI, 0.70-0.99).7 Women taking tamoxifen showed no difference in mortality or recurrence risk associated with soy intake.
An additional small prospective cohort study (n=256) found similar reductions in recurrence and mortality associated with higher consumption of soy protein.8