We have recently reported that phagocytosis of killed Saccharomyces cerevisiae, baker's yeast, induced apoptosis in human breast cancer cell lines MCF-7, ZR-75-1 and HCC70. In this study we have evaluated the effect of treatment with MGN-3, a modified arabinoxylan from rice bran, on phagocytosis and yeast-induced apoptosis in breast cancer cells. Cancer cells were cultured with yeast at a ratio of 1:10 in the absence or presence of MGN-3, and the percentages of phagocytic and apoptotic cancer cells were examined by flow cytometry and by cytospin preparations. Cancer cells treated with MGN-3 exhibited increased percentages of attachment (200%) and uptake of yeast (313%) by MCF-7 cells at 0.5 hr, as compared with cells without MGN-3. In addition, treatment with MGN-3 resulted in a 2 fold increase in the percentage of apoptotic MCF-7 cells, 2.5 fold for ZR-75 cells and 1.8 fold for HCC70 cells. MGN-3 effect was dose-dependent and associated with increased activation of caspases 8 and 9 in MCF-7 cells, and caspases 8, 9 and 3 in HCC70 cells. This data demonstrates that MGN-3 accelerates phagocytosis-induced apoptosis of cancer cells, which may represent a novel therapeutic strategy for the treatment of breast cancer.