Soy Powder Does Not Appear to Reduce Recurrences in Prostate Cancer

Soy powder following a radical prostatectomy does not appear to reduce biochemical recurrences among men with high-risk prostate cancer. These results were recently published in JAMA.

Prostate is a common cancer among men in the United States. Some types of prostate cancer – those that are fairly small within the prostate and slow-growing according to several measurable markers – can often be left with no treatment for several years without causing any harm. However, other types of prostate cancer are considered more aggressive (high-risk); these are the types that are ultimately responsible for the majority of deaths related to prostate cancer.

A radical prostatectomy is a standard therapeutic procedure among men with high-risk prostate cancer. It is a surgical procedure in which the prostate is entirely removed. Following surgery, patients are monitored for cancer recurrences.

One way in which to measure recurrences is to test blood levels of the prostate specific antigen (PSA). The test measures PSA levels, which are small proteins shed by the prostate tissue and/or prostate cancer cells. If PSA levels rise at a certain rate following surgery, or reach certain levels, patients are considered to have a biochemical recurrence.

Soy products have been suggested to reduce the risk of recurrences among men with prostate cancer. To further explore this concept, researchers recently conducted a clinical trial at 7 United States centers involving 177 men diagnosed with high-risk prostate cancer. The men underwent a radical prostatectomy and then received either soy powder supplement or placebo (calcium caseinate) following surgery for approximately 2 years.

There was no significant difference in the rates of biochemical recurrence among the group of men who received soy versus placebo at 2 years (27.2% for those on soy and 29.5% for those on placebo).
The researchers concluded that “Daily consumption of a beverage powder supplement containing soy protein isolate for 2 years following radical prostatectomy did not reduce biochemical recurrence of prostate cancer in men at high risk of PSA failure.”

However, soy supplementation in different forms or doses, or in those with low- or intermediate-risk prostate cancer may produce different effects. Future trials are warranted to answer these questions.

Reference: Bosland M, Kato K, Zeleniuch-Jacquotte A, et al. Effect of Soy Protein Isolate Supplementation on Biochemical Recurrence of Prostate Cancer After Radical Prostatectomy: A Randomized Trial. JAMA. 2013;310(2):170-178. doi:10.1001/jama.2013.7842