High Omega-3, Low Omega-6 Diet With Fish Oil for Men With Prostate Cancer on Active Surveillance: The CAPFISH-3 Randomized Clinical Trial

PURPOSE Men on active surveillance (AS) for prostate cancer are extremely interested in dietary changes or supplements to prevent progression of their disease. We sought to determine whether a high omega-3, low omega-6 fatty acid diet with fish oil capsules (D + FO) decreases proliferation (Ki-67) in prostate biopsies in men with prostate cancer on AS over a 1-year time period. METHODS In this phase II, prospective randomized trial, men (N = 100) with grade group 1 or 2 prostate cancer who elected AS were randomly assigned to the D + FO or a control group. Same-site prostate biopsies were obtained at baseline and 1 year. The primary end point was the change in Ki-67 index from baseline to 1 year from same-site biopsies compared between the groups. RESULTS The Ki-67 index decreased in the D + FO group by approximately 15% from baseline to 1 year (1.34% at baseline, 1.14% at 1 year) and increased in the control group by approximately 24% from baseline to 1 year (1.23% at baseline, 1.52% at 1 year), resulting in a statistically significant difference in the change of Ki-67 index between the groups (95% CI, 2% to 52%, P = .043). There was no significant difference in the secondary outcomes grade group, tumor length, Decipher genomic score, or prostate-specific antigen between the two groups. Four patients in the D + FO group were withdrawn from the trial because of adverse events related to the FO. CONCLUSION A high omega-3, low omega-6 diet with FO for 1 year resulted in a significant reduction in Ki-67 index, a biomarker for prostate cancer progression, metastasis, and death. These findings support future phase III trials incorporating this intervention in men on AS.