A new epidemiological study on the relation between soy isoflavones and breast cancer has recently been published (Caan et al. 2011).
3088 breast cancer survivors from the United States were followed for a median of 7.3 years. Cancer recurrence and mortality were correlated with isoflavone intake. Patients were distributed to five subgroups, with the lowest group consuming no isoflavones and the highest group consuming 13.3 to 86.9 mg daily.
None of the isoflavone consuming women had a higher risk of mortality or cancer recurrence when compared with the zero-intake group. In the contrary there was a trend towards an improved cancer survival and recurrence rate with increasing dietary intake of isoflavones (p = 0.02), with a 54 percent reduction in risk of death in the highst quintile. The same trend was also found in women who took tamoxifen - there was no indication of an adverse interaction between tamoxifen use and soy isoflavone consumption. The receptor status of the breast cancer did likewise not play any role.
This study is now the fourth epidemiological study (Guha et al. 2009; Shu et al. 2009; Wu et al. 2008) to report no adverse effects of isoflavone consumption on breast cancer prognosis, with two of these studies performed in a Western country. The authors conclude that “these studies provide the necessary epidemiological evidence that clinicians no longer need to advise against soy consumption for women with a diagnosis of breast cancer”.
