Soy isoflavones and risk of cancer recurrence in a cohort of breast cancer survivors: the Life After Cancer Epidemiology study

Abstract

Purpose Soy isoflavones, structurally similar to endogenous estrogens, may affect breast cancer through both hormonally-mediated and non-hormonally related mechanisms. Although the effects of soy are not well understood, some breast cancer survivors increase their soy intake post-diagnosis in attempt to improve their prognosis. Therefore, we examined the role of soy isoflavone intake and the risk of breast cancer recurrence by hormone receptor status, menopausal status, and tamoxifen therapy. Materials and methods A cohort of 1954 female breast cancer survivors, diagnosed during 1997–2000, was prospective followed for 6.31 years and 282 breast cancer recurrences were ascertained. Isoflavone intake was assessed by mailing modified Block and supplemental soy food frequency questionnaires to participants, on average 23 months post-diagnosis. Risk of breast cancer recurrence, measured by hazard ratios (HR) and 95% confidence intervals (CI), was estimated using multivariable delayed-entry Cox proportional hazards models. Results Suggestive trends for a reduced risk of cancer recurrence were observed with increasing quintiles of daidzein and glycetin intake compared to no intake among postmenopausal women (P for trend: P = .08 for daidzein, P = .06 for glycetin) and among tamoxifen users (P = .10 for daidzein, P = .05 for glycetin). Among postmenopausal women treated with tamoxifen, there was an approximately 60% reduction in breast cancer recurrence comparing the highest to the lowest daidzein intakes (>1453 micrograms (µg)/day versus < 7.7 µg/day) (HR, 0.48; 95% CI, 0.21–0.79, P = .008). Conclusion Soy isoflavones consumed at levels comparable to those in Asian populations may reduce the risk of cancer recurrence in women receiving tamoxifen therapy and moreover, appears not to interfere with tamoxifen efficacy. Further confirmation is required in other large prospective studies before recommendations regarding soy intake can be issued to breast cancer survivors.

Post-diagnosis Soy Food Intake and Breast Cancer Survival: A Meta-analysis of Cohort Studies

“…After reading full-texts, we excluded reviews (n =47), experimental studies (n =88) and not about survival (n=41). Finally, five cohort studies (six citations (Guha et al, 2009;Shu et al, 2009;Kang et al, 2010;Caan et al, 2011;Nechuta et al, 2012;Zhang et al, 2012)) (11206 patients) were included.…”

“…Regarding to the associations between soy food intake after cancer diagnosis and survival (mortality or recurrence), the results were not the same based on available cohort studies (Guha et al, 2009;Shu et al, 2009;Kang et al, 2010;Caan et al, 2011;Nechuta et al, 2012;Zhang et al, 2012). One meta-analysis of four prospective cohort studies (Boyapati et al, 2005;Fink et al, 2007;Guha et al, 2009;Shu et al, 2009) showed that soy isoflavones intake was inversely associated with risk of breast cancer recurrence (Dong et al, 2011). However, two (Boyapati et al, 2005;Fink et al, 2007) of them investigated whether soy intake prior to cancer diagnosis might be associated with breast cancer survival, and the rest (Guha et al, 2009;Shu et al, 2009) evaluated whether soy intake after cancer diagnosis might be associated with breast cancer survival.…”

“…And another study conducted by Fink et al (Fink et al, 2007) reported that reduced hazard ratios [hazard ratio (95% confidence interval)] for all-cause mortality were observed among premenopausal and postmenopausal women for the highest quintile of intake prior to cancer diagnosis, compared with the lowest, for isoflavones [0.52 (0.33-0.82)]. Regarding to the associations between soy food intake after cancer diagnosis and survival (mortality or recurrence), the results were not the same based on available cohort studies (Guha et al, 2009;Shu et al, 2009;Kang et al, 2010;Caan et al, 2011;Nechuta et al, 2012;Zhang et al, 2012). One meta-analysis of four prospective cohort studies (Boyapati et al, 2005;Fink et al, 2007;Guha et al, 2009;Shu et al, 2009) showed that soy isoflavones intake was inversely associated with risk of breast cancer recurrence (Dong et al, 2011).…”

“…One meta-analysis of four prospective cohort studies (Boyapati et al, 2005;Fink et al, 2007;Guha et al, 2009;Shu et al, 2009) showed that soy isoflavones intake was inversely associated with risk of breast cancer recurrence (Dong et al, 2011). However, two (Boyapati et al, 2005;Fink et al, 2007) of them investigated whether soy intake prior to cancer diagnosis might be associated with breast cancer survival, and the rest (Guha et al, 2009;Shu et al, 2009) evaluated whether soy intake after cancer diagnosis might be associated with breast cancer survival. This meta-analysis did not conduct subgroup analysis of the time of soy foods intake (prior to cancer diagnosis vs. after diagnosis).…”

“…This meta-analysis did not conduct subgroup analysis of the time of soy foods intake (prior to cancer diagnosis vs. after diagnosis). Meanwhile, one of the four included studies focused on survival (Fink et al, 2007), and the other three focused on recurrence (Boyapati et al, 2005;Guha et al, 2009;Shu et al, 2009). So whether soy intake after cancer diagnosis might be associated with breast cancer survival (including mortality or recurrence) deserved a further meta-analysis.…”