The aim of the present study was to determine the effect of carotenoids on the cell cycle and cell viability in human breast cancer cell lines. Human breast cell lines were treated with carotenoids (0.5-10 μM) for 48 and 96 h. Cell viability was monitored using the MTT method (3-[4,5dimethylthiazol-2-yl]-2,5- diphenyltetrazolium bromide; thiazolyl blue). The cell cycle was analyzed by flow cytometry, and apoptotic cells were identified by annexin/propidium iodide (PI) biomarkers