the underlying preventive mecha- nism remains to be determined. Moreover, it is not known whether there are any differences in lycopene activity among different subtypes of human breast cancer cells. Using ER⁄PR positive MCF-7, HER2-positive SK-BR-3 and triple-negative MDA-MB-468 cell lines, we investigated the cellular and molecular mechanism of the anticancer activity of lycopene. Lycopene treatment for 168 consecutive hours exhibited a time-dependent and dose-dependent anti-proliferative activity against these cell lines by arresting the cell cycle at the G0⁄G1 phase at physiolog- ically achievable concentrations found in human plasma. The greatest growth inhibition was observed in MDA-MB-468 where the sub-G0⁄G1 apoptotic popula- tion was significantly increased, with demonstrable cleavage of PARP. Lycopene induced strong and sustained activation of the ERK1⁄2, with concomitant cyclin D1 suppression and p21 upregulation in these three cell lines. In triple negative cells, lycopene inhibited the phosphorylation of Akt and its downstream mole- cule mTOR, followed by subsequent upregulation of proapoptotic Bax without affecting anti-apoptotic Bcl-xL. Taken together, these data indicate that the pre- dominant anticancer activity of lycopene in MDA-MB-468 cells suggests a poten- tial role of lycopene for the prevention of triple negative breast cancer.