Does a High-Veggie Diet a Day Keep Prostate Cancer Progression at Bay?

Hello, I am Dr Gerald Chodak for Medscape. Today's topic is findings from the Men's Eating and Living (MEAL) study that were presented by Parsons and colleagues^[1] at the 2018 American Urological Association's annual meeting in San Francisco.

The MEAL study was a prospective, randomized [phase 3] clinical trial to assess whether or not a dietary intervention prevents disease progression of [localized prostate cancer in patients] on active surveillance for low-risk disease.

Patients between the ages of 50 and 80 years were eligible to participate in the trial, provided they had at least a 10-core biopsy in which no more than 25% of the cores showed cancer and no one core contained more than 50% of cancer. Participants aged 70 years and younger had a Gleason score of 3+3, and participants older than age 70 years had a Gleason score of 3+4 [or less]. The clinical stage for all participants was [T1c] or T2a, and their prostate-specific antigen (PSA) levels were less than 10 ng/mL.

The trial outcomes were measured in terms of disease progression, which was defined as an increase in PSA over 10 ng/mL, a PSA doubling time of less than 3 years, or pathologic changes showing progression on a follow-up prostate biopsy. The intervention group received telephone-based counseling to modify their dietary intake, which included increasing vegetable consumption and decreasing meat consumption. The control group simply received a booklet on managing localized prostate cancer.

The follow-up period demonstrated that the patients [in the counseling group implemented the recommended] dietary changes by increasing their intake of carrots and tomatoes [as well as other vegetables and legumes] and by reducing their intake of meat. Unfortunately, [despite patient compliance], the MEAL study failed to find a clinically significant difference in [short-term] disease-progression rates.

I have several important concerns about the design of this trial. First of all, it may be that the men [in this study] were simply too healthy, or their disease was not aggressive enough to [demonstrate] progression during the follow-up period. In other words, the patients enrolled [in the study] were so low-risk that it [made it difficult] to detect improvement in the progression rate of disease by dietary intervention.

Another concern I have relates to the manner in which the study outcomes were measured. For example, if a participant's PSA was 9.8 ng/mL at the time of enrollment but rose to 10.1 ng/mL [during the study period], this patient would be considered to have disease progression. Yet, we know very well that the long-term outcome in a scenario such as this may not result in a poor outcome.

The other issue [regarding] measuring outcome could be that we need a better way to assess whether or not disease progression is occurring in the short-term. Ultimately, long-term survival is the outcome we really want, but that kind of study would take a much longer time to design.

The following may be another problem: that it is simply too early to detect a benefit, even if there is one. Longer follow up may be needed.

The study results [from the MEAL trial] are somewhat disappointing. Perhaps other dietary interventions are needed—ones that include certain vitamins, herbs, and other supplements, along with dietary changes. Perhaps other dietary modifications are required to truly assess whether or not [such interventions] can affect disease progression in patients with low-risk prostate cancer. Hopefully, going forward, we will see more studies of this type. Active surveillance is becoming increasingly popular, and at least 50% of all patients with newly diagnosed prostate cancer are potentially eligible [for this management option]. Hopefully, that will be forthcoming.

I look forward to your comments. Thank you.

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