Weekly Health Update:
Soy Isoflavones & Recurrent Prostate Cancer
By, Robert A. Wascher, MD, FACS
The information in this column is intended for informational purposes only, and does not constitute medical advice or recommendations by the author. Please consult with your physician before making any lifestyle or medication changes, or if you have any other concerns regarding your health.
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SOY ISOFLAVONES & RECURRENT PROSTATE CANCER
The interest level in natural and complementary treatments for cancer has never been higher in the medical and scientific communities than it is now. For decades, now, this area of research was often relegated to the fringes of the clinical research community, while most mainstream academic research centers and Big Pharma companies focused on the design and testing of new biochemical therapies with improved therapeutic and safety profiles. With the 5-year overall survival rate among all patients with cancer approaching a record 65 percent, we have, unquestionably, made enormous improvement in our ability to cure many of the cancers that, not too long ago, were associated with a very high risk of death. Cancer physicians also have far more effective medications available now to control the noxious side effects of many of our “front-line” cancer therapies, which have had the beneficial effect of further reducing suffering and morbidity among thousands of cancer patients as they undergo their daily treatments.
Despite the admirable (and ongoing) progress that has been achieved over the past four decades in cancer care, however, nearly 600,000 cancer patients will still succumb to their disease this year in the United States, alone. Thus, more effective cancer prevention strategies are necessary to reduce the number of new cases of cancer, and more effective (and less toxic) cancer therapies must be identified. Moreover, with the annual cost of many new cancer therapies now running into the hundreds-of-thousands of dollars per patient, per year, our already unsustainable (and still rising) health care costs demand that the cancer care community rigorously evaluate less costly approaches to cancer prevention and treatment.
Because so-called “natural products” are relatively inexpensive, widely available, and generally non-toxic, there is a growing interest in studying these agents using the same high-level prospective, randomized clinical trials that are routinely used by pharmaceutical companies and academic medical centers to evaluate promising new drug therapies. Because of their great complexity and high cost, however, randomized clinical trials are best reserved for studying novel therapies for which there is at least some laboratory (“preclinical”) or early-phase clinical data available that suggests some potential benefit to humans. Until recently, however, and most likely due to inherent biases against natural products by the mainstream clinical research community in the past, very little high-level clinical research has been performed to definitively evaluate natural products as disease prevention and treatment agents. Fortunately, and despite shrinking research funding over the past decade, there has been a recent surge in the number of large randomized, prospective, controlled clinical research trials reporting their findings of the effects of natural products on disease prevention and treatment.
As the vast majority of natural products and lifestyle-related research in the past has been based upon low-powered research methods, it should come as no surprise that recent high-level prospective clinical research studies have, more often than not, found little or no benefit associated with the use of many of these supplements and products. (Moreover, in some cases, several very popular and highly recommended vitamins and dietary supplements have actually been found to be potentially harmful.) However, a great deal of promising high-level clinical research has yet to be done in order to fully and accurately assess the, literally, hundreds of natural products for which there is at least some preclinical data supporting potentially beneficial health effects. (In my forthcoming book, “A Cancer Prevention Guide for the Human Race,” I will be comprehensively reviewing and analyzing the available laboratory and clinical research data on natural products and lifestyle strategies as an integral approach to a cancer prevention lifestyle. The publication of this groundbreaking and authoritative evidence-based cancer prevention guide is tentatively scheduled for May of this year.)
In many respects, prostate cancer is the male counterpart of breast cancer in women. Analogous to breast cancer in women, prostate cancer is the most common cancer that occurs in men (excluding minor skin cancers), and the second most common cause of cancer death. In 2009, an estimated 192,000 new cases of prostate cancer were diagnosed in the United States alone, and approximately 27,000 American men died of this disease in the same year. In most industrialized nations, prostate cancer accounts for approximately 25 percent of all cancer diagnoses in men (similar to the percentage of breast cancer cases among all cancer cases diagnosed in women).
A newly published prospective, early-phase, clinical pilot study from Canada evaluated the effects of a soy beverage (“soy milk”) on the progression of recurrent prostate cancer in 29 men following radiation therapy for their cancers. This study, which has just been published in the journal Nutrition and Cancer, was not a placebo-controlled randomized study, however, this small phase II clinical study prospectively followed these patient volunteers for 6 months, during which time serial measurements of the level of prostate-specific antigen (PSA) in their blood was performed (PSA is the primary prostate tumor marker that is measured both to detect early prostate cancer and to identify recurrences of this type of cancer.)
The time interval during which the level of PSA in the blood doubles is an important indicator of the rate of progression of recurrent prostate cancer. In this small prospective clinical pilot study, the consumption of approximately one quart (500 ml) of soy beverage per day, for 6 months, was associated with an actual decline in PSA levels in 4 (14 percent) of these patient volunteers, while another 8 (28 percent) of these recurrent prostate cancer patients experienced a greater than 100 percent increase in their PSA doubling times. Another 5 patients (17 percent) experienced a 50 percent or greater improvement in their PSA doubling times during the 6 month duration of this study. Thus, during the brief duration of this intriguing small pilot study, nearly 60 percent of men with early recurrence of their prostate cancer experienced either a decrease in the biochemical extent of their recurrent cancers or a significant biochemical slowing of the progression of their recurrent disease.
Whether or not longer durations of soy intake will be able to sustain the impressive results of this study is not clear at this time. More importantly, whether or not these observed favorable effects of daily soy intake on PSA levels and PSA doubling times will actually translate into prolonged survival (or not) is also unknown at this time. It will require several larger and longer-term randomized, placebo-controlled, blinded, prospective clinical trials of soy foods and soy isoflavone supplements to answer these critical questions (several of which are already underway). Meanwhile, the overall safety profile for moderate amounts of soy intake in men appears to be quite favorable, and so many prostate cancer experts are cautiously recommending soy-derived foods for men with prostate cancer, and for men who are at an increased risk of developing prostate cancer, pending the completion of these larger prostate cancer research studies.
For a much more detailed and comprehensive evaluation of the role of soy foods, and other dietary supplements and lifestyle modifications, in the prevention of prostate cancer (and other cancers), look for the publication of “A Cancer Prevention Guide for the Human Race ” in the spring of this year.
I and the staff of Weekly Health Update would like to take this opportunity to thank the more than 100,000 new and returning readers who have visited our premier global health information website this month, alone. As always, we enjoy receiving your feedback and questions, and I continue to try to personally answer as many of your inquiries as I possibly can.
Disclaimer: As always, my advice to readers is to seek the advice of your physicianbeforemaking any significant changes in medications, diet, or level of physical activity
Dr. Wascher is an oncologic surgeon, professor of surgery, cancer researcher, oncology consultant, and a widely published author
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(Anticipated Publication Date: May 2010)
Copyright 2007 - 2010
Robert A. Wascher, MD, FACS
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Title: Soy Isoflavones & Recurrent Prostate Cancer
Testosterone Supplements in Frail Elderly Men
Keywords: soy, prostate cancer, recurrence, prevention, isoflavones
testosterone supplements, men, elderly, frail, muscle, bone