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jc3737 posted:
Intake of Soy Isoflavones on Breast Cancer Recurrence.
Source: Canadian Medical Association Journal
Breast cancer is a cancer that forms in tissues of the breast, usually the ducts (tubes that carry milk to the nipple) and lobules (glands that make milk). It occurs in both men and women, although male breast cancer is rare. Risk factors for breast cancer include gender, age, family history, defective genes, early onset of menstruation, late menopause and late childbearing. Breast cancer is about ninety percent due to genetic abnormalities that happen as a result of the aging process and the "wear and tear" of life in general.
Soy Isoflavones are a dietary supplement derived from soybeans containing phytoestrogens. These weak estrogens are chemically similar in structure to naturally produced estrogen hormones. Isoflavones are found in soy foods both with and without a sugar molecule attached. The two primary isoflavones in soybeans are daidzein and genistein and their respective glucosides, genistein and daidzein. Soy foods typically contain more genistein than daidzein, although this ratio varies among the different soy products. In cultures where soy products are consumed in abundance, women's health problems, certain cancers, and cardiovascular disease are reported to be less prevalent.
A current study sought to investigate the effect of soy isoflavones on the recurrence of breast cancer in patients receiving endocrine therapy. The study included 524 women who were followed for a median of 5.1 years. The researchers found that intake of soy isoflavones had no effect on death rate in premenopausal patients. However, it was discovered that high dietary intake of soy isoflavones was associated with a significantly lower risk of recurrence in post-menopausal women with estrogen and progesterone receptor positive breast cancer and those who were receiving endocrine therapy. These results suggest that soy isoflavones may be beneficial for some post-menopausal women who have undergone treatment for breast cancer.1
1 Kang X, Zhang Q, Wang S, et al. Effect of soy isoflavones on breast cancer recurrence and death for patients receiving adjuvant endocrine therapy. CMAJ. Nov2010;182(17):1857-62,
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heretk responded:
Something seems to be wrong with their stats. If you look at the table 2:



( http://www.cmaj.ca/content/182/17/1857/T2.large.jpg )


The "p for trend" in the 3 columns out of 4 is 0.46,0.87 and 0.76 and only in one column (the third) it is 0.02! That is in spite of the fact that the statistical samples in each subgroup (bin) was similar, that is about 20 cases out of 50 to 70 total.

To remind us what it means, P is the probability that the results are purely by a chance. P value of 0.05 or less is regarded as the accepted threshold of being "statistically significant".

I suspect that their p=0.02 was some calculation artefact (*) or error and all results are in fact not statistically significant.

Heretic

*) Note that the sample size of 20 cases implies about plus minus 20% error bar while the effect itself is of the order of -12% to -33% in terms of Hazard Ratio reduction - comparable to the error bar itself. That is more consistent with the p of 0.46-0.87 rather than p=0.02.


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