TheL-sulforaphane (SFN) component of broccoli sprout showed anticancer activity in several preclinical studies including breast cancer. Estrogens are considered major risk factors in breast carcinogenesis. The aim of this study was to evaluate the effect of SFN on the expression of cytochrome P450 involved in the estrogen metabolism in breast cancer cell lines MCF7 and MDA-MB-231 and in non-tumorigenic MCF10A cell line. The expression ofCYP19, CYP1A1, 1A2, 1B1was determined at the transcript and protein levels. There were found some remarkable differences in the effect of SFN at a dose of 5 μmol/L onCYP19expression: in ER(+) MCF7 significant reduction, in ER(−) MDA-MB-231 an increased expression and unchanged expression in MCF10A cell line. The effect of SFN on CYPs (1A1, 1A2, 1B1) involved in estrogen catabolism was to a lesser extent dependent on breast cell line. The slightly reduced CYP1A1 protein level was observed in all cell lines tested. An increased level of CYP1A2 and decreased level ofCYP1B1expression were found in MCF10A. These results indicate that the naturally occurringLisomer of SFN may affect the expression of P450s involved in estrogen metabolism. This effect may contribute to the anticancer activity of SFN in breast tissue. Copyright © 2014 John Wiley & Sons, Ltd.