Indole-3-carbinol (I3C) is an essential nutrient found in Brassica vegetables, such as broccoli, cauliflower, and collard greens. Diindolylmethane (DIM) is the digestion derivative of indole-3-carbinol via condensation formed in the acidic environment of the stomach. If you are going to use I3C as a nutritional supplement (and you may want to consider this after reading this article), take DIM.
Diindolylmethane has long been studied for its anti-carcinogenic effects and its ability to bind and rid the body of “bad” estrogens. These so-called “bad” estrogens are both made in the body as intermediate metabolites and consumed through estrogen exposure in drinking water and estrogen disruptors such as plastics. The latter is termed xenoestrogens, as there are toxins from environmental sources.
Beating Cancer with Nutrition
A well-nourished cancer patient can better manage the disease. Cancer is the number two cause of death in America and the developed nations of the world with one out of four dying from cancer and 38% of women and 43% of men projected to develop cancer over their lifetime. While the overall death rate from cancer has not appreciably declined since the start of the multi-trillion dollar war on cancer in 1971, there is good news from the nutrition arena. Optimal nutrition can reduce the risks of developing cancer by up to 90%, hence it is a strong preventative tool for everyone.
DIM’s history for cancer prevention and therapy began when a mouse study showed its promising results in tobacco smoke, carcinogen-induced, lung adenocarcinoma.  DIM was found to have “lung cancer preventive effects” mediated via modulation of the receptor tyrosine kinase/PI3K/Akt-signaling pathway.  DIM demonstrated “exceptional anti-cancer effects against hormone responsive cancers like breast, prostate and ovarian cancers.” 
In a recent study, it was concluded that DIM rather than I3C was the active agent in cell culture studies destroying cancer. 
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Diindolylmethane transduces signaling via aryl hydrocarbon (Ah) receptor, NF-κB/Wnt/Akt/mTOR pathways, to help inhibit growth. These pathways are typically up-regulated in cancer patients yet DIM may help block many of these avenues.
DIM also was found to induce cell cycle arrest, helping slow replication of cancer cells. It also helps modulate key CYP enzymes in the liver, aiding important detoxification channels. DIM was found to alter angiogenesis, the lay-down of new vessels that cancers rely on for continued growth. It decreases cell invasion, metastasis and epigenetic behavior of cancer cells as well. 
Diindolylmethane was found to induce Nrf2-mediated, intercellular detoxification (GSTm2, UGT1A1, and NQO1) and antioxidant (HO-1 and SOD1) genes. These pathways are our essential detoxification pathways inside every cell. Think of them as the cellular garbage service that gets rid of the poisons that would otherwise wreak havoc. Individuals with genetic defects on Nrf2, Glutathione, and SOD genes have an even greater need to support such cellular garbage service.
Also, DIM has shown synergistic benefits with isothiocyanates, and sulforaphane, the nutrients found in cruciferous vegetables that have been found to have such wonderful benefits for patients with cancer. 
Overall, Diindolylmethane showed anti-cancer properties, especially in hormonally driven tumors. DIM is currently in clinical trials for various other forms of cancers. However, given its benefits to boost other natural therapies, it may be a good addition for all cancer patients.