Dietary Changes to Reduce Diabetes Risk May Also Increase Survival for Breast Cancer

Women with breast cancer who adhered to a diet to reduce their risk for diabetes had improved survival compared with those who did not follow this specific diet, according to findings presented during the 2020 San Antonio Breast Cancer Symposium.

Diabetes may be common in women with breast cancer, especially since 75%, or more than 2.6 million women, are at least 60 years or older, “which means breast cancer survivorship must be managed in consideration with aging-related comorbidity such as diabetes,” said Wang during the presentation. Type 2 diabetes, in particular, is a risk factor for breast cancer incidence and may be a predictive factor for breast cancer mortality. In addition, breast cancer increases the likelihood of developing type 2 diabetes.

“Identifying modifiable strategies to prevent type 2 diabetes among breast cancer survivors may be very important to improve their survival outcomes,” said Tengteng Wang, a research fellow at Harvard T.H. Chan School of Public Health, during the virtual presentation of the study.

Researchers analyzed data from 8,320 women with stage 1 to 3 breast cancer from two large cohort studies: Nurses’ Health Study (1980-2014) and the Nurses’ Health Study II (1991-2015). Validated questionnaires were completed every two to four years to collect information on diet among other factors.

This study focused on a diabetes risk reduction diet with nine dietary components including higher intakes of nuts, cereal fiber, coffee, polyunsaturated-saturated fat ratio and whole fruits, in addition to a lower glycemic index of diet and lower intakes of sugar-sweetened beverages/fruit juices, trans fat and red meat.

“The (diabetes risk reduction diet) has been associated with 14% lower type 2 diabetes risk in (a) previous publication of the Nurses’ Health Study,” said Wang.

Researchers calculated an average score of adherence to this diabetes risk reduction diet through repeated measures of diet after a diagnosis of breast cancer. Follow-up was conducted for a median of 16 years after cancer diagnosis.

During follow-up, 2,146 deaths occurred, of which 948 were related to breast cancer. Women with higher diet adherence scores after diagnosis had a 33% lower risk for all-cause mortality and a 17% lower risk for mortality related to breast cancer compared with women with lower diet adherence scores.

“Our results did not differ by breast tumor (estrogen receptor) status or stage,” said Wang.

During the discussion portion of the presentation, Wang said that she and her colleagues analyzed what may be the potential mechanism for this association. She said, “We looked at how (diabetes risk reduction diet) influenced gene expression in (the) breast tumor for (a) subgroup of our breast cancer patients, and … according to our pathway analysis, the (diabetes risk reduction diet) is more associated with the pathway related to immune regulation and also cell proliferation, so this is, I think, an interesting finding.”

When neighborhood socioeconomic status was considered, the association between diet adherence and mortality risk was slightly affected, with patients with greater adherence having a 31% lower risk for all-cause mortality and a 14% lower risk for mortality from breast cancer.

Women who improved their adherence to a diabetes risk reduction diet after breast cancer diagnosis had a lower risk for breast cancer mortality compared with those with consistently low adherence to this diet.

“In conclusion, we felt that a greater adherence to the (diabetes risk reduction diet) after breast cancer diagnosis was associated with better survival outcomes, which means promoting dietary changes consistent with prevention of type 2 diabetes may be very important for breast cancer survivors,” said Wang.

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