 This study examined the effect of folic acid, FA, on breast cancer, BC, risk. It found that FA had differential effects on BC cells depending on their phenotype. Specifically, FA caused changes in gene expression in non-transformed MCF10A cells, while it had no effect on cancerous MCF7 or HS578T cells. Additionally, FA affected the expression of genes involved in apoptosis, cell death and senescence in MCF10A cells, while increasing the expression of genes related to cell proliferation in both MCF7 and HS578T cells. Furthermore, the levels of expression of folate transporter genes were also differentially affected by FA in each cell line. Overall, this study suggests that physiologically relevant concentrations of FA may have differential effects on BC cells based on their phenotype, which could explain why there is still some uncertainty about its effect on BC risk. This article was authored by Arjordan Price, Paranayla LeCrop and Graham C. Boj.