RESUMEN
<p><b>OBJECTIVE</b>To investigate the heterogeneity of human breast cancer cells, their influence on biological behavior of tumor cells and clinical implications.</p><p><b>METHODS</b>The subpopulations of MCF-7 breast cancer cells were isolated by Percoll gradient centrifugation. DNA content and cell cycle distribution were detected with flow cytometry. Tumor chemosensitivity analysis was performed with MTT assay.</p><p><b>RESULTS</b>Heterogeneity was observed in DNA content and cell cycle distribution among four subpopulations of breast cancer cells, which were related to their proliferation ability and chemosensitivity results.</p><p><b>CONCLUSION</b>Hereditary instability and intrinsic characteristics of most tumor cells, not only lead to tumor progression and heterogeneity but also cause the loss of monoclonality and the generation of subclones. Further study on some profiles of tumor heterogeneity such as DNA content, cell cycle distribution and their influence on tumor proliferation and chemosensitivity may very well improve the clinical treatment.</p>