Can Diet Influence Prostate Cancer Progression?

Roxanne Nelson, BSN, RN

April 11, 2018

Can diet modification reduce prostate cancer progression in men undergoing active surveillance?

An ongoing study is slated to answer just that question. Importantly, the investigators have already shown that it is feasible to implement a large-scale phase 3 clinical trial of the use of diet for patients with prostate cancer, with appropriately balanced study arms, a racially diverse cohort, and national representation from both academic and community settings.

In an article published in BJU International, the authors report on the ability to enroll prostate cancer patients who are undergoing active surveillance in the Men's Eating and Living (MEAL) study, which is a study of dietary intervention.

Bigger news is due very soon, as the study has been completed, explained lead author J. Kellogg Parsons, MD, a professor of urology at the University of California, San Diego. "The results will be presented next month at the upcoming American Urological Association's 2018 annual meeting in San Francisco," Parsons said.

The goal was to have men with prostate cancer who are undergoing active surveillance increase their consumption of vegetables. "We were trying to prevent the disease from progressing and...reduce the number of men having to go on treatment," he said.

Parsons explained that the groundwork for this trial began in the mid-2000s. His group was the first to conduct a national trial of diet modification. It was initially piloted in a small group of prostate cancer patients.

Preclinical and epidemiologic research has demonstrated that diet may influence the risks for prostate cancer incidence, progression, metastases, and mortality. "Very small proof-of-principle studies have also shown that diet can decrease the risk of developing prostate cancer," he told Medscape Medical News.

Although the results of the current study are not yet available, Parsons noted that with the pilot studies that were conducted, "we noticed that men ate less fat and less meat, because they were eating more vegetables. Men were coming back and telling us how good they felt."

Subjective data are difficult to measure, and the pilot studies were too small to draw conclusions, Parsons explained. "But we looked to see if we could actually change men's diets in the pilot, because otherwise, there was no point in moving forward with a larger study," he said. "And we appeared to be doing that."

Will Success Be Elusive?

In an accompanying editorial, Laurence Klotz, MD, from the Division of Urology, Sunnybrook Health Sciences Center, Toronto, Canada, refers to the number of studies that have failed to show a benefit regarding diet or dietary supplements.

"Many epidemiological studies have pointed to the benefits of fruit and vegetable intake high in vitamin E, selenium, beta carotene, lycopene and other micronutrients, and a diet low in animal fat," Klotz writes.

However, "several pivotal studies have taken the bloom off the rose of prevention," he emphasizes. He describes negative studies, such as the SELECT trial, which found not only that there was no benefit to supplements but that supplements actually increased the risk of developing prostate cancer.

Results of studies of the association between fruit and vegetable consumption and prostate cancer have also been inconsistent. As an example, Klotz cites a large observational study of more than 130,000 men that found no significant association between fruit and vegetable intake, including consumption of cruciferous vegetables, and prostate cancer (Int J Cancer. 2004;109:119-24).

But despite negative studies, "a lingering spark of hope exists that the many positive population, epidemiological, and preclinical studies supporting dietary approaches to prevention will be vindicated," he says. "The MEAL study in the current issue of BJU Int is, therefore, a laudable and ambitious initiative."

Although the initiative is laudable, Klotz writes that he suspects that MEAL may face an insurmountable hurdle regarding the study's primary endpoint — risk for disease progression.

"To be meaningful, prevention studies in men on surveillance should therefore identify, at the very least, a real reduction in grade progression, based on state-of-the-art evaluation at baseline with MRI and targeted biopsies as warranted, and long-term follow-up," he writes.

However, a decline in the rate of volume progression of Gleason 6 tumors, which is a major endpoint of this study, is not meaningful. "In the study as described, which does not explicitly incorporate MRI, an imbalance in the number of patients having off-protocol MRI and targeted biopsies between the two arms could significantly bias the outcome," Klotz argues.

In addition, there are problems related to long-term dietary intervention studies in general. There are "well-known methodological limitations in this area, namely, ensuring long-term compliance, recall bias of food intake, and contamination of the control arm," he says.

Parsons acknowledges the criticism of the study's endpoints in the Klotz editorial, noting that he knew the study would be criticized on those grounds. "I disagree with it," he said. "But I am looking forward to the debate about it — I welcome the debate."

The study was supported by the National Cancer Institute, the Department of Defense, and the Prostate Cancer Foundation. The authors and Dr Klotz have disclosed no relevant financial relationships.

BJU Int. 2018;121:534-539; 487-488. Abstract, Editorial

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