Aim: The low bioavailability of curcumin, a polyphenol, limits its use as an antitumor agent. Identifying mechanisms to improve the bioavailability and effectiveness of curcumin can modify utilization of other plant-derived phenolic compounds. This study was conducted with an aim to determine the influence of some flavonoids on the effects of curcumin in an HL-60 cell line. Methods: Cells were incubated in the presence of different concentrations of curcumin and several flavonoids for 20 h. Cytotoxicity was evaluated using propidium iodide staining. The evaluation of γH2AX expression using a specific antibody, together with study of the cell cycle, was analyzed using flow cytometry. Results: A synergistic effect was obtained only using a combination of curcumin and lower concentrations of epicatechin. The low concentration of quercetin exerted an additive effect only in combination with curcumin. Moreover, incubation with curcumin and epicatechin resulted in a significant increase in the γH2AX level. Conclusion: Combination treatment with epicatechin and curcumin can potentially be considered for improving the effectiveness and bioavailability of curcumin in cell lines of myeloid leukemia.