CYP1B1 and breast cancer: It was previously reported that 5 μM of arsenite not only decreases phenobarbital (PB)-induced CYP3A23 protein, with a little to no decrease in CYP3A23 mRNA, in primary cultures of rat hepatocytes (51) but also decreases CYP1A1 and CYP1A2 expression in primary human hepatocytes (55), benzo[a]pyrene-induced CYP1A1 and CYP1B1 expression in T-47D human breast-cancer cells (56), and benzo[k]-fluoranthene-mediated induction of CYP1A1 mRNA in HepG2 cells (57).