Three poster studies at the San Antonio Breast Cancer Symposium presented new data on associations between dietary nutrients and breast cancer.
The main findings were that (1) soy isoflavones appear to be protective against breast cancer; (2) renewed effort may be needed to encourage women with early breast cancer to supplement their diet with calcium and vitamin D; and (3) omega-3 fatty acids appear to potentiate the efficacy of tamoxifen.
Soy Isoflavones & Breast Proliferation
Some years ago, nutritional experts suggested that eating soy products would be beneficial for bone health and for alleviation of menopausal symptoms, such as hot flashes and vaginal dryness. Subsequent reports suggested consumption of soy products might be associated with an increased risk of breast cancer.
Many patients with a history of breast cancer have resorted to soy products to alleviate postmenopausal symptoms as an alternative to hormone-replacement therapy; yet there are no definitive data on the safety of soy products in this group.
A year-long pilot study reported at the Symposium found that consumption of soy isoflavones did not increase cell proliferation in breast cancer survivors.
“Our findings suggest no negative effects [of soy isoflavones] and perhaps even a beneficial effect,” stated Melanie E. Palomares, MD, MS, a staff physician at City of Hope National Medical Center.
The study enrolled 23 postmenopausal women with a history of unilateral breast cancer: Stages I-II or ductal carcinoma in situ (DCIS). Their median age was 57.
Women were randomized to receive either isoflavone tablets 50 mg b.i.d. or placebo tablets for one year. Treatment was adhered to (as assessed by pill count and urinary genistein levels) by 93% in the isoflavone group and 87% in the placebo group.
For the 19 evaluable patients, at six months the Ki67 index (a measure of epithelial proliferation) dropped in the isoflavone group by 3.1% from baseline compared with 0.9% in the placebo group.
At 12 months, the Ki67 index continued to decrease in both groups: 4.9% from baseline in the isoflavone group and 4.1% in the placebo group.
At baseline, hyperplasia was observed in the contralateral breasts in 44% of subjects. “Less than 5% of normal postmenopausal women would have hyperplasia. We think the increased hyperplasia seen at baseline reflects the higher risk of our subjects,” Dr. Palomares noted.
Serial biopsy revealed no significant differences in breast tissue between the treatment groups. Additionally, no significant differences were seen between the groups with regard to expression of hormone receptors.
Dr. Palomares said that in another study comparing soy isoflavone tablets and placebo in breast cancer survivors, she and her colleagues found a decrease in the number of hot flashes at three and six months.
“Our pilot studies suggest that soy products are safe,” she said.
Calcium & Vitamin D Supplementation
Adjuvant chemotherapy and hormonal therapy can have a negative impact on bone health in patients with breast cancer. The recommendation is that patients take 1,000 to 1,500 mg of calcium plus 200 to 600 mg of vitamin D, depending on age and menopausal status.
A retrospective study conducted at Memorial Sloan-Kettering Cancer Center found that only 10% of 100 patients with early breast cancer were taking calcium and vitamin D supplementation.
“A lot of our patients were taking alendronate and assumed that they did not need other supplements,” said Rachel S. Zinaman, RD. “We decided to look at patients with early breast cancer and, shockingly, only 10% of our sample were meeting the goal of the recommended intake of calcium and vitamin D. Even those women who were taking calcium were not always taking vitamin D.”
Women who finished adjuvant therapy were more likely to be taking adequate supplementation with calcium and vitamin D than those still undergoing treatment,” Ms. Zinaman noted. “Perhaps they believe that their treatment is behind them, and they want to focus on building up their health.”
As a result of this study, a new system has been put in place at the MSKCC Breast Center to track calcium and vitamin D supplement intake for all new patients and at patient visits.
“Even if patients are coming in to discuss side effects of chemotherapy, we ask them about supplement intake,” Ms. Zinaman said. Consultations with new patients about upcoming chemotherapy include education about the need for calcium and vitamin D, she added.
“Clinicians who are part of the health team will be able to make an intervention at this level to ensure adequate calcium and vitamin D intake,” added another of the authors, Catherine H. Van Posnak, MD, an assistant clinical physician.
The study enrolled 100 patients. At the time of the initial nutrition consultation, 60 patients were receiving adjuvant chemotherapy, 18 were receiving adjuvant hormonal therapy, 13 patients had no systemic adjuvant therapy planned, and nine had completed adjuvant therapy. Data were based on chart reviews of nutritional consultations.
Omega-3 Fatty Acids Enhance Tamoxifen Response
A diet rich in omega-3 fatty acids increases the efficacy of tamoxifen, according to the results of an animal study reported by William Friedrichs, a research scientist at the University of Texas Health Science Center at San Antonio.
“A potential mechanism for this effect is either direct or indirect inhibition of m-TOR, a pathway involved in cell proliferation,” he said. “These data suggest that dietary intervention may hold promise in the treatment of endocrine resistance in breast cancer. Further study is needed to determine optimal dose of omega-3 fatty acids.”
In the study, mice were implanted with breast cancer cells in the mammary fat pad. Then they were divided into two dietary groups: those given a diet of corn oil (which is rich in omega-6 fatty acids) and those given fish oil (rich in omega-3 fatty acids).
Animals in each group were further subdivided to receive either tamoxifen or placebo treatment. The diets rich in omega-3 fatty acids restored therapeutic response to tamoxifen in breast tumors with high Akt activity (Akt activity is associated with aggressive disease and tamoxifen resistance).
Tumor response corresponded with a decrease in mTOR activity and cell proliferation. Mr. Friedrichs said that he and his co-investigators are now seeking funding for a clinical trial.