Diet quality indices are associated with breast cancer by molecular subtypes in Mexican women.

Background: Inconclusive epidemiological evidence suggests that diet quality indices may influence breast cancer (BC) risk; however, the evidence does not consider the molecular expression of this cancer.

Purpose: We aimed to evaluate if diet quality is related to molecular subtypes of BC, in women residing in Northern Mexico.

Methods: This is a secondary analysis of 1,045 incident cases and 1,030 population controls from a previous case-control study, conducted between 2007 and 2011 in Northern Mexico. Information about the expression of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 (HER2) was obtained from medical records to classify BC as luminal (ER + and/or PR+/HER2-), HER2+ (ER+/-and/or PR+/-/HER2+), or triple-negative (TN) (ER- and PR-/HER2-) cases. Food consumption was assessed with a semi-quantitative food frequency questionnaire. Diet quality was evaluated using the Mexican Diet Quality Index (MxDQI) and the Mexican Alternative Healthy Eating Index (MxAHEI). We used unconditional logistic regression models to estimate the association between Mexican diet quality indices and BC molecular subtypes.

Results: The MxDQI was related to lower odds of BC (OR_T3vsT1=0.24; 95%CI: 0.18, 0.31). Similarly, MxAHEI was negatively associated with BC (OR_T3vsT1=0.43; 95%CI: 0.34, 0.54). The associations of both indices remained significant in the ER + and ER- tumors, and in the BC luminal and HER2 + molecular subtypes, except in the TN molecular subtype for MxAHEI, which was not statistically significant.

Conclusions: Our findings showed that MxDQI and MxAHEI were negatively associated with BC risk regardless of its molecular subtype.