NEW ORLEANS — The adoption of a low-fat dietary pattern significantly reduced the risk for death from any cause after breast cancer diagnosis, according to the results of a secondary analysis of a randomized trial presented at the American Association for Cancer Research Annual Meeting.
Deaths attributed to breast cancer were somewhat lower in the dietary group.
However, doubts remain about the extent of protection conferred by dietary changes, according to Rowan T. Chlebowski, MD, PhD, professor of medicine at David Geffen School of Medicine at UCLA and chief of hematology and oncology at Harbor–UCLA Medical Center.
“There is a nearly 50-year-old concept across countries that [reduction of] dietary fat intake may lead to a reduction in breast cancer incidence,” Chlebowski said during his presentation. “Fifty years ago, studies showed lower incidence and death rates after World War II in certain Asian countries, compared with the United States or United Kingdom.”
The randomized Women’s Health Initiative Dietary Modification trial included 48,835 postmenopausal women aged 50 to 79 years with no history of breast cancer and a dietary fat intake greater than 32%.
Women assigned to the dietary intervention group (n = 19,541) were given a fat gram goal by a trained dietician, and a low-fat dietary plan was implemented. The researchers monitored 4-day food record at baseline, and a food frequency questionnaire was administered at baseline, after 1 year, and then every 3 years thereafter during follow-up.
Women assigned to the control group (n = 29,294) received a dietary guideline report but were not asked to make dietary changes.
After a mean follow-up of 8.3 years, the researchers observed 1,767 incident breast cancers (diet, n = 672; control, n = 1,095).
Fewer incident breast cancers (HR = 0.92; 95% CI, 0.84-1.01) and deaths from disease (HR = 0.77; 95% CI, 0.48-1.22) occurred in the dietary group, but the differences were not statistically significant.
The secondary analysis included two primary outcome measures — deaths from breast cancer and deaths after breast cancer, defined as mortality from any cause among those diagnosed with the disease — during the mean 8.3years of the dietary intervention.
Chlebowski and colleagues also assessed breast cancer OS — defined as survival after breast cancer diagnosis, with death from any cause — among the 1,767 study participants diagnosed with breast cancer during the dietary intervention period.
Both study groups had similar baseline characteristics and breast cancer risk factors, and participants in both groups underwent screening mammography at comparable rates throughout follow-up.
The researchers observed a greater decrease in dietary fat intake (–9.5% vs. –1.3%; P < .001), as well as increased consumption of fruits and vegetables (1.5 vs. 0.4; P < .001) and grains (–.05 vs. –1; P < .001), in the dietary intervention group.
Women in the dietary group demonstrated a lower rate of death from breast cancer (HR = 0.68; 95% CI, 0.43-1.07), as well as a significantly reduced rate of deaths of any cause after breast cancer (40 vs. 94; HR = 0.65; 95% CI, 0.45-0.94).
The mean follow-up for women diagnosed with breast cancer was 10.9 years. In this group, those assigned to the dietary intervention group demonstrated a higher rate of 10-year breast cancer OS (82% vs. 78%; HR = 0.8; 95% CI, 0.66-0.97).
A temporal trend analysis of dietary modification influence on breast cancer OS showed a more favorable effect during the dietary intervention period than after (P = .02 for interaction).
The researchers had cause of death information for 400 women with breast cancer. The leading causes of death were breast cancer (diet, n = 65; control, n = 111), other cancer (diet, n = 31; control, n = 51), cardiovascular disease (diet, n = 19; control, n = 55) and other causes (diet, n = 51; control, n = 97).
“In a breast cancer prevention trial, adopting a low-fat diet reduced deaths after breast cancer and increased breast cancer OS,” Chlebowski said. “Yet, analyses suggest that continued dietary intervention is needed to maintain this benefit. We believe that these secondary findings ... provide evidence supporting an association between dietary change and breast cancer outcomes.”
Chlebowski RT, et al. Abstract CT041. Presented at: American Association for Cancer Research Annual Meeting; April 16-20, 2016; New Orleans.
Prentice RL, et al. JAMA. 2006;doi:10.1001/jama.295.6.629.
Chlebowski reports consultant and/or speakers bureau roles with Amgen, Genentech, Genomic Health, Novartis and Novo Nordisk.