So far, no study has shown a direct association between the development of breast cancer and moderate consumption of soy milk. It was first believed that the two were linked because of the isoflavones found in soy. Isoflavones are plant estrogens, and there have been studies linking high estrogen levels to an increased risk of breast cancer. However, soy products generally don't contain high enough amounts of isoflavones that would pose a significant risk. You know what they say: everything in moderation!