Low-Fat Diet May Reduce Breast Cancer Recurrence Risk

ORLANDO-Decreasing breast cancer survivors' dietary fat reduced the rate of disease recurrence by 24%, according to a study presented by Rowan T. Chlebowski, MD, PhD, at the American Society of Clinical Oncology 41st Annual Meeting (abstract 10). "A lifestyle intervention resulting in dietary fat reduction may increase relapse-free survival in a population of mostly postmenopausal breast cancer patients," said Dr. Chlebowski, chief, Division of Medical Oncology and Hematology, Harbor-UCLA Medical Center.

Dr. Chlebowski and his colleagues conducted the randomized, prospective Women's Intervention Nutrition Study (WINS) to evaluate the role of dietary fat in breast cancer recurrence and whether an intense dietary intervention influenced disease-free survival. The investigators enrolled 2,437 women, ages 48 to 79, with early-stage breast cancer (stage I to IIIa) within 1 year of primary surgery at 37 clinical centers from 1994 to 2001.

Patients had received standard breast cancer management: surgery with or without radiation therapy. Estrogen-
receptor (ER)-negative patients received chemotherapy. ER-positive patients received tamoxifen with chemotherapy as an option.

Patients were randomized 40% to the intervention and 60% to the control group. The 975 women in the intervention group received individual counseling from a registered dietitian during eight 1-hour sessions. The counseling instructed the women how to decrease dietary fat while maintaining a nutritionally adequate meal plan.

The recommended diets were not designed to cause weight loss or require dramatic dietary changes, and included decreasing use of margarine or oil in cooking, eliminating baked goods and snack chips, and decreasing meat portion size. The 1,462 women in the control group received less frequent counseling about nutritionally adequate diets.

Women in the intervention group attended group sessions every 3 months. Researchers monitored dietary fat intake during telephone contacts twice annually. Controls also met with a dietitian every 3 months to ensure they were consuming a nutritionally adequate diet. Median follow-up was 60 months.

At baseline, both groups of women consumed about 56 g of fat daily, getting about 30% of their calories from fat. At 1 year, women in the intervention group decreased their dietary fat intake by 40% to 33 g/d (20% of daily calories from fat) and lost 4 pounds; they reported finding the diet satisfying and maintained their dietary fat intake in the range of 33 to 34 g/d for the 5 years of follow-up. Women in the control group only slightly decreased their fat intake from what they consumed at baseline and had a slight weight gain at the end of the study.

At 60 months, 277 women experienced relapse events, 9.8% of women in the intervention group vs 12.4% of women in the control group. "Relapse-free survival was significantly longer in patients in the diet group, compared to the control group (hazard ratio, 0.76)," Dr. Chlebowski said. "The absolute difference in relapse-free survival is about 3% at year 6." Disease-free survival was also significantly longer in the dietary intervention group. There was no significant difference in overall survival.

Dr. Chlebowski analyzed results by body mass index, nodal involvement, and ER status subgroups. Body mass index was not statistically significant, and there was no difference between women with node-positive and node-negative cancers. There was no significant difference between groups among those with ER-positive disease. However, Dr. Chlebowski found a 42% relative reduction in risk of recurrence (P = .018) and an 8% absolute risk reduction at year 6 in women with ER-negative tumors.

He noted that the ER-negative subgroup included only 478 patients, that the analysis was not preplanned, and that the results must be interpreted with caution and are hypothesis-generating only. Additional research will be needed to determine why this may have occurred, said Dr. Chlebowski, who suspects it may have to do with insulin or inflammatory marker levels.

"Dietary intervention targeting dietary fat intake may influence breast cancer recurrence risk, but we believe further follow-up in this population is needed," Dr. Chlebowski commented.

During the discussion, Eric P. Winer, MD, of the Dana-Farber Cancer Institute, called the results tantalizing. "The magnitude of the effect seen here is similar to that of many widely accepted interventions," said Dr. Winer, adding that further follow-up will be needed. Dr. Winer thought the etiology of the response could be related to the decrease in dietary fat, the substitution of other nutrients in place of fat, weight loss, or a combination of factors.

"I think we can tell our patients preliminary evidence suggests that a low-fat diet and/or weight loss may lower recurrence risk, but at this time the evidence is insufficient to recommend that postmenopausal women with breast cancer routinely pursue dietary fat reduction," Dr. Winer said. "However, based on the WINS results and extensive observational research, it is prudent for breast cancer survivors to lose weight if overweight and to avoid weight gain after a diagnosis of breast cancer."