In this prospective cohort study of early-stage breast cancer survivors, increasing adherence to a prudent dietary pattern, characterized by high intakes of fruits, vegetables, legumes, whole grains, low-fat dairy products, poultry, and fish, was associated with a decreasing risk of overall death and death from causes other than breast cancer. In a complementary trend, increasing consumption of a Western dietary pattern consisting of high intakes of red and processed meats, refined grains, sweets, high-fat dairy products, snacks, and butter was related to an increasing risk of overall death and death from causes other than breast cancer. In contrast, neither dietary pattern was associated with risk of breast cancer recurrence or death from breast cancer. Women who tended to follow the prudent dietary pattern were more physically active, whereas women who had greater adherence to the Western dietary pattern were more likely to be overweight or obese and gained more weight (on average, 6 lb) after diagnosis. The corresponding protective and deleterious effects of a prudent diet and Western diet, respectively, on survival did not vary markedly by these or other modifiable lifestyle factors.
Although several studies have investigated the role of dietary patterns in relation to risk of primary breast cancer,17,32–38
to our knowledge, only the NHS23
has examined the impact of this measure of diet on breast cancer survival in a cohort of 2,619 women over a median follow-up time of 9 years since diagnosis. Our results agree with the NHS findings in that women who followed a more prudent diet had a decreased risk of death from causes other than breast cancer, whereas those who followed a more Western diet had an increased risk of death from causes other than breast cancer. Our death rates (56.6% as a result of breast cancer and 44.4% as a result of other causes after a median of 6.3 years of follow-up) were similar to those of the NHS (58.5% as a result of breast cancer and 41.5% as a result of other causes after a median of 9 years of follow-up). Among women who died of non–breast cancer causes in our study (n = 98), 29.6% died of CVD, 17.3% died of other cancers, and 53.1% died of causes aside from CVD and cancer, compared with rates of 22%, 45%, and 33%, respectively, in the NHS. Also similar to the NHS, we found no association between either of the dietary patterns and risk of death from breast cancer. Although the NHS did not observe an association between dietary patterns and risk of overall death, our study noted an inverse relationship of increasing adherence to the prudent dietary pattern and decreasing risk of all-cause mortality and a direct relationship of increasing adherence to the Western dietary pattern and increasing risk of all-cause mortality.
Our results are consistent with the NHS23
and studies of diet and cardiovascular disease12,15
and suggest that dietary patterns may represent a more important factor in the etiology of overall health and outcomes not related to breast cancer, as opposed to outcomes related to breast cancer. In fact, previous studies have reported somewhat modest and/or mixed associations of specific foods and/or food groups in relation to breast cancer prognosis.39
Furthermore, in another analysis from the LACE Study, no association was observed between postdiagnosis weight gain (which is strongly correlated with increasing adherence to the Western dietary pattern and weaker adherence to the prudent dietary pattern in the present study) and breast cancer–related outcomes.40
Strengths of the LACE study include being one of the few existing cohorts of early-stage breast cancer survivors and one of the first studies to comprehensively examine the association between dietary patterns and breast cancer recurrence and survival. Although our analyses rely on self-report of diet on the FHCRC-FQ, this questionnaire has been validated in the Women's Health Initiative.26,41
Cause-specific mortality may have been misclassified on death certificates from which we extracted cause of death information. Although misclassification of cause of death has been an issue in most studies of cause-specific mortality, it is somewhat reassuring that our findings regarding deaths not associated with breast cancer are consistent with results from the NHS.23
Because the LACE cohort consists of early-stage breast cancer survivors who were enrolled on average 2 years after diagnosis, we would not be able to detect associations with breast cancer death if the associations were only related to deaths that occurred in the immediate survivorship period (within 2 years) but not in the extended survivorship period (after 2 years). Finally, our results are not generalizable to women diagnosed with advanced-stage breast cancer and apply only to women who have survived, on average, 2 years since diagnosis.
In summary, we found that higher consumption of prudent and Western dietary patterns are associated with decreased and increased risks of overall death and death from causes other than breast cancer, respectively, but the patterns had no association with risk of breast cancer recurrence or breast cancer–related deaths. These results indicate that although dietary habits may not influence breast cancer–related outcomes for women diagnosed with breast cancer, they are nonetheless strong predictors of overall prognosis after breast cancer diagnosis. Consistent with dietary guidelines directed towards the general population for overall chronic disease or cancer prevention,42–44
women diagnosed with early-stage breast cancer may benefit from dietary patterns that include healthier foods such as fruits, vegetables, whole grains, and poultry and less consumption of red meat and refined foods.