Effect of imatinib and doxorubicin on apoptosis of breast cancer cells. Cells were incubated with imatinib, doxorubicin alone or their combination for 24 and 48 hours. Apoptotic fraction was estimated by TUNEL assay and apoptotic cells were counted using fluorescence microscopy. For each sample, a total of five times 200-500 cells were scored and apoptotic fractions are expressed as percentage of total cells counted. Apoptotic cells show a green nuclear staining compared to vital cells.