From the San Antonio Breast Cancer Symposium

San Antonio—A very-low-fat diet greatly reduces the risk for breast cancer recurrence among women with early breast cancer, particularly among those with hormone-receptor—negative tumors, according to the results of the Women’s Intervention Nutrition Study (WINS), which were presented at the San Antonio Breast Cancer Symposium.

Referring to the 24% increase in breast cancer relapse-free survival among the women following a low-fat diet compared with those following a standard diet, Eric P. Winer, MD, of the Dana-Farber Cancer Institute, commented at the meeting that the WINS results were “tantalizing,” noting that “this preliminary evidence suggests that a low-fat diet and/or weight loss may lower recurrence risk.”

This phase 3 clinical trial was sponsored by the National Cancer Institute and was initiated based on data from previous preclinical and observational studies suggesting that fat intake may be related to breast cancer outcomes.

This randomized, prospective study enrolled 2437 women from 37 US clinical sites. Participants were postmenopausal women with early breast cancer who had undergone surgery, with or without radiation therapy, and received systemic therapy with tamoxifen (Soltamox) or chemotherapy.

Patients were randomized within 1 year of surgery to a dietary intervention program (n = 975) to reduce fat intake, or to the control arm (n = 1462). Baseline characteristics between the arms were similar, but slightly more patients in the dietary intervention group had mastectomy rather than breast-conserving surgery.

After 5.8 years of follow-up, 22% fewer deaths occurred among the group of women consuming a low-fat diet, though this difference was not statistically significant.

But in a subset of 362 women with estrogen-receptor (ER)-negative and progesterone-receptor (PR)-negative disease, the difference was very significant: In this hormone-negative group, mortality risk was reduced by 66% (P = .003) with the low-fat diet, resulting in an 11% absolute difference (6% vs 17%, respectively) with dietary intervention compared with the standard diet.

The recurrence rate was reduced by 54% with the low-fat diet among women with ER- and PR-negative disease but by only 8% among women with hormone-positive disease. In the overall population, relapses were reduced by 21%, which was of borderline significance. 

“These results suggest there may be something that patients with breast cancer can do themselves, with the assistance of trained dietary professionals, to reduce their recurrence risk,” said lead investigator Rowan T. Chlebowski, MD, PhD, of Harbor-UCLA Medical Center, Torrance, Calif.

The goal of the dietary intervention was to reduce dietary fat intake to 15% of total calories. Women attended 8 biweekly, 1-hour dietary counseling sessions, kept a food diary, talked with dietitians every 3 months, and, if desired, attended monthly support group sessions. Women in the control group met with a dietitian at the start of the study and were phoned by a dietitian every 3 months.  

Mean daily fat intake at baseline was about 56 g for each arm, which was about 30% of total calories. At 1 year, fat intake was reduced to 33 g/day, to about 20% of total calories, in the dietary intervention group, but was maintained at 51 g/day (or about 29% of total calories) in controls. These differences were sustained through year 5.

Weight loss was also a significant benefit of the low-fat diet. Women in the intervention group lost a mean of  1.1 kg/m² in body mass index and an average of 6 lb more than those in the control group during 5 years (P for both <.005).

Discussing the role of diet in breast cancer, Dr Chlebowski stressed that the strongest data indicate total fat reduction rather than substitution of one kind of fat for another.  

The investigators acknowledged that the dietary intervention was quite strict and may not be appropriate for all patients. “I think when patients are really motivated and asking what they can do, the clinician can tell them that dietary intervention is something to consider. Nutritional support could cost around $1000,” Dr Chlebowski commented.  

Dr Chlebowski added, “A lifestyle intervention that reduces fat intake with moderate influences on body weight may improve relapse-free survival of breast cancer patients receiving conventional cancer management. Our exploratory analyses suggest there is a differential effect of the dietary intervention, based on hormonal receptor status.”

Kent Osborne, MD, director of the Breast Cancer Center at Baylor College of Medicine, Houston, said, “The results of WINS are as good as, or better than, any treatment intervention we have for breast cancer. If these data are confirmed, this is a striking effect.”

Dr Winer added that although it is premature to recommend that all postmenopausal women follow such a diet, he is “convinced there is enough information about weight and breast cancer that, if you are interacting with a woman who has been diagnosed with breast cancer and is significantly overweight or is likely to gain weight with therapy, it is something worth having a conversation about.”