Beyond The Abstract Dietary Modification In Patients With Prostate Cancer On Active Surveillance: A Randomized, Multi Centre Feasibility Study
Prostate cancer patients in large numbers are experimenting with complementary and alternative medicine, including diet [19]. Assessing the clinical efficacy of dietary change is an important public health issue and requires the accumulation of data from rationally-designed trials focused on feasible diet-based interventions. Unlike the present study, the intensive lifestyle modifications and face-to-face counseling employed in the prior study of diet and active surveillance patients [15] requires substantial resource commitments that may be difficult to implement and sustain on a larger scale.
Diet change represents an innovative approach to refining treatment paradigms for lower risk prostate cancer. Active surveillance patients are a particularly compelling study population in this regard for several reasons. First, approximately 100,000 men are diagnosed with lower-risk prostate cancer every year in the U.S.; thus, treatment benefits for this population would have important ramifications for public health. Second, because up to 30% of men on active surveillance may progress [7], reducing this proportion represents a realistic therapeutic goal. Third, these patients are not receiving active therapy (i.e., radiation, surgery, or androgen deprivation) that would otherwise obscure or confound beneficial effects of dietary change on prostate cancer progression. Finally, these patients would likely be receptive to relatively simple nutritional interventions with proven benefits to cardiovascular and overall health.
Indeed, because prostate cancer diagnosis is a source of considerable anxiety and diminished quality of life for many patients diagnosed with lower-risk disease [20], it is possible that dietary change would not only exert therapeutic biological effects, but would also encourage men with lower risk prostate cancer and no signs of progression to remain in an active surveillance program. Many patients with no objective PSA or pathologic criteria for progression will nonetheless opt for treatment [7]. Treatment preferences in this situation are generally believed to arise from patient discomfort over not receiving curative therapy for a cancer diagnosis.
For these patients, a diet change program presents an opportunity to alter their perceptions of lower risk prostate cancer by providing an intervention or therapy on which to focus, thereby easing their discomfiture and possibly dissuading otherwise lower risk men from pursuing unnecessarily aggressive, morbidity-generating treatments. Such an approach would promulgate a novel therapeutic paradigm for lower risk prostate cancer akin to diet alterations for non-insulin dependent diabetes: medical management, without curative intent, of a chronic disease state.
Our innovative telephone-based counseling program focuses on beneficial dietary components associated with decreased prostate cancer incidence and progression. The counseling protocol is step-wise and phased; it employs strategies adopted from social cognitive theory [21, 22] using the techniques of motivational interviewing [23]. It is practicable, demands few resource commitments for the patient, and is low-cost for relatively large study populations. A similar program has proved efficacious in breast cancer patients: the Women's Healthy Eating and Living (WHEL) Study produced significant diet changes and plasma carotenoid increases over 12 months that have been maintained for 4 years in over 1,500 women previously diagnosed. The significance of the plasma carotenoid increases in the intervention group is underscored by a comparison of these results to those of another major dietary intervention: the Polyp Prevention Trial [25]. Although MEAL study participants began with total carotenoid concentrations 30% higher than those of Polyp Prevention Trial participants, the proportional increase in intervention group carotenoid concentrations in MEAL was almost twice that achieved in the first year of the Polyp Prevention Trial.
Several caveats of these results are worth addressing. First, although dietary self-reporting methods may be susceptible to systematic measurement error [26], plasma carotenoid concentrations are an effective biomarker for dietary intake of carotenoids and serve as an objective indicator of a vegetable-intense diet [27]. Moreover, carotenoids have been associated with reduced risk of incident prostate cancer [28, 29] and diminished oxidative damage in prostate tissue [30].
Second, while these results do not prove that the changes in diet intake and plasma carotenoid concentrations observed over a 6-month period will be maintained over a longer period of time, the WHEL Study findings suggest that diet changes observed in the first 6 months of this intervention will be maintained for at least 4 years [24].
Third, although these results do not prove that changes in diet and plasma carotenoid concentrations will necessarily alter the natural history of prostate cancer, it is reasonable to hypothesize that these diet changes increased total vegetable, cruciferous vegetable, and tomato intakes will decrease disease progression in active surveillance patients, given the extensive observational and pre-clinical data supporting this concept. Moreover, it is important to note that the rationale for trials of diet intervention and prostate cancer is driven not only by the supposition that diet plays a significant role in prostate cancer carcinogenesis, but also by the widespread desire of patients to know whether dietary change has any value in disease control.
Finally, although PSA concentrations did not change appreciably during the duration of the study, this trial was neither powered nor designed to examine PSA changes as a primary endpoint, which would require determination of PSA kinetics (doubling time or velocity) over a longer time period [7]. Our main purpose in this feasibility study was to test the hypothesis that a telephone-based counseling intervention would produce diet and plasma carotenoid changes in prostate cancer patients not to assess whether these changes would alter the natural history or clinical progression of prostate cancer in an active surveillance population.
In summary, these data support the feasibility of implementing clinical trials of telephone-based dietary interventions in men with prostate cancer on active surveillance. Future, larger studies should utilize PSA changes as a primary endpoint to test the hypothesis that telephone-based diet changes will decrease disease progression and need for conventional treatment in these patients.
References
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J. Kellogg Parsons, MD, MHS
Assistant Professor of Surgery/Urology
Staff Investigator Moores Cancer Center
University of California San Diego
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Dincolo de abstract dietetice Modificari la pacienþii cu cancer de prostatã pe active de supraveghere: Un studiu randomizat, multi Centrul de studiu de fezabilitate - Beyond The Abstract Dietary Modification In Patients With Prostate Cancer On Active Surveillance: A Randomized, Multi Centre Feasibility Study - articole medicale engleza - startsanatate