Effects of Commercially Available Soy Products on PSA in Androgen-deprivation-naïve and Castration-resistant Prostate Cancer

Monika Joshi, MD; Nicole M. Agostino, MD; Rebecca Gingrich, MSN; Joseph J. Drabick, MD, FACP


South Med J. 2011;104(11):736-740. 

In This Article

Patients and Methods

The clinical records of 10 men treated with soy products for biochemically relapsed prostate cancer (low but rising PSA levels) were reviewed. Three men also had been receiving maximum ADT and had rising PSA levels that were consistent with CR disease. These three patients continued on ADT while receiving soy products. Scans showed no gross metastatic disease. Assent to a trial of soy was obtained from each patient before starting them on soy products, and the information was documented in each patient's clinical chart. The men were advised to drink 8-oz glasses of soy milk as the preferred soy source 3 times per day, but other sources of soy could be used if taken more than 3 times per day. Almost all of our patients consumed the same brand of soy milk (Silk, WhiteWave Foods, Broomfield, CO). Adherence was assessed by direct questioning during each clinic encounter and was documented in each patient's medication history. For PSA kinetics to be derived, patients needed at least three PSA determinations per state of treatment, that is, presoy versus during soy. PSA kinetics (PSA velocity, PSA doubling time, and slope of PSA vs time curves) were calculated using the Memorial Sloan-Kettering Cancer Center PSA kinetics calculator. For PSA levels <0.1 ng/mL, a PSA level of 0.1 was assigned to allow calculation of the kinetics using the calculator. We also calculated the percentage of decline of PSA in responding patients by dividing the nadir PSA while receiving treatment with soy by the pretreatment PSA level, multiplying by 100, and subtracting from 100.


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