Tamoxifen has no effect on p21. Restoration of these growth regulators is extremely important. Tumor suppressor p53, for example, works through the p21 that I3C restores. I3C also inhibits cancers caused by other types of chemicals. If animals are fed I3C before exposure to cancer-causing chemicals, DNA damage and cancer is virtually eliminated.
Similar results happen in the liver.
And in a study from New York University Medical Center, female smokers taking 400 mg of I3C significantly reduced their levels of a major lung carcinogen. Cigarette chemicals are known to adversely affect estrogen metabolism. There is no proven breast cancer prevention. I3C beat out more than 80 other substances, including tamoxifen, for anticancer potential in one assay. They claim that the indoles, which down-regulate estrogen receptors, can be used to treat and prevent cancer and autoimmune diseases such as multiple sclerosis, arthritis, and lupus.