In one, in MCF-7 cells, an estrogen receptor (ER) positive breast cancer cell line, that were treated with 5 μM of B[a]P for 24 hours, expression of the tumor suppressor breast cancer gene (Brca) 1 was downregulated and protein expression of the tumor suppressor gene P53 was upregulated [19]. This evidence concerns the gene ESR1 and breast cancer.