Abstract
Forkhead box protein A1 (FOXA1) promotes luminal differentiation, and hypermethylation of the gene can be a mechanism of developing estrogen receptor-negative (ER
) breast cancer. We examined FOXA1 in breast tumor and adjacent normal tissue in relation to reproductive factors, particularly higher parity and no breastfeeding, that are associated with ER
tumors.
We performed IHC for FOXA1 in breast tumors (
= 1,329) and adjacent normal tissues (
= 298) in the Women's Circle of Health Study (949 Blacks and 380 Whites). Protein expression levels were summarized by histology (H) scores. Generalized linear models were used to assess FOXA1 protein expression in relation to reproductive factors by ER status.
ER-positive (ER
) versus ER
tumors had higher FOXA1 protein expression (
< 0.001). FOXA1 expression was higher in tumor versus paired adjacent normal tissue in women with ER
or non-triple-negative cancer (both
< 0.001), but not in those with ER
or triple-negative cancer. Higher number of births (1, 2, and 3+) was associated with lower FOXA1 protein expression in ER
tumors [differences in H score, or β = -8.5; 95% confidence interval (CI), -15.1 to -2.0], particularly among parous women who never breastfed (β = -10.4; 95% CI, -19.7 to -1.0), but not among those who breastfed (β = -7.5; 95% CI, -16.9 to 1.8). The associations for ER
tumors were similar, although they were not statistically significant.
In this tumor-based study, higher parity was associated with lower FOXA1 expression in ER
tumors, and breastfeeding may ameliorate the influence.
These findings contribute to our understanding of FOXA1 methylation and breast cancer etiology.