Study Shows Modestly Reduced Breast Cancer Recurrence Risk With Increased Protein Intake Independent of Tumor Insulin Receptor Status
In an analysis in the Nurses’ Health Study population reported in the Journal of Clinical Oncology, Holmes et al found modest reductions in the risk for distant recurrence of breast cancer with greater protein intake. No associations with intake of essential amino acids, branched-chain amino acids, or leucine or with tumor expression of insulin receptor were observed.
Higher protein intake has been associated with improved breast cancer survival in several prospective studies, including a study in 1,982 women in the Nurses’ Health Study. The current study involved 6,348 women diagnosed with stages I to III breast cancer between 1976 and 2004, with follow-up through 2010. A total of 1,046 distant recurrences were observed.
Inverse Association With Recurrence
An inverse association between postdiagnosis energy-adjusted protein intake and distant recurrence was observed. On multivariate analysis, the relative risks for the second to fifth (highest intake) quintiles of protein intake vs the first quintile (lowest intake) were 0.95 (95% confidence interval [ CI] = 0.79–1.15), 0.92 (95% CI = 0.76–1.11), 0.75 (95% CI = 0.61–0.91), and 0.84 (95% CI = 0.69–1.03; P = .02 for trend). For animal protein intake, the relative risks were 0.88 (95% CI = 0.73–1.06), 0.85 (95% CI = 0.70–1.02), 0.75 (95% CI = 0.62–0.92), and 0.78 (95% CI = 0.63–0.95; P = .003 for trend). Recurrence-free survival was 94.0% vs 92.1% at 5 years and 87.4% vs 83.3% at 10 years for the highest vs lowest quintile of total protein intake.
The association of reduced recurrence risk with increased protein intake did not appear to be explained by the intake of essential amino acids, branched-chain amino acids, or any individual amino acid, and the association did not differ according to the presence or absence of tumor insulin receptor. There was also no clear association of any particular protein-containing foods with the reduction in recurrence risk.
Association With Survival
Results for breast cancer death were similar to those for recurrence but appeared to be less robust due to fewer outcomes. On multivariate analysis, relative risks were 1.00, 0.97, 0.74, and 0.95 for the lowest vs increasing quintiles of total protein intake (P = .17 for trend) and 0.87, 0.85, 0.77, and 0.85 for the lowest vs increasing quintiles of animal protein intake (P = .044 for trend).
The investigators concluded: “We found a modest survival advantage with higher intake of protein, regardless of [insulin receptor] status. There was no clear mechanism for this association, although it is consistent with prior studies. Our data suggest that there is likely no advantage for women with a history of breast cancer in restricting protein intake or protein-containing foods.”
The study was supported by grants from the National Institutes of Health.
Michelle D. Holmes, MD, of Brigham and Women’s Hospital, is the corresponding author of the Journal of Clinical Oncology article.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
