A chemical in vegetables such as broccoli, cauliflower and cabbage, as well as another one found in soy, can increase DNA repair in cells. This could prevent them from becoming cancerous. Links have already been established between eating certain vegetables and a reduction in cancer risk. These findings suggest a mechanism for why that might be the case.
Vegetables such as broccoli contain a compound called I3C, and one called genistein is present in soy beans. These two chemicals increase the amount of BRCA proteins present in cells. These proteins prevent damaged genetic material from being passed from one generation of cells to the next. Cancer cells typically contain low amounts of BRCA proteins, and faulty BRCA signaling heightens one's risk of some cancers, including prostate, breast, and ovarian. 
From LEF:
For Cellular Protection & Optimal Hormone Balance
It is a sad fact that the very hormones we need to stay young can cause adverse effects as we age. Consumption of cruciferous vegetables, however, can favorably alter one's hormone profile.
Scientists have identified specific extracts from cruciferous vegetables (broccoli, cauliflower, Brussels sprouts, etc.) that modulate hormones in a way to help maintain healthy cell division. For instance, animal studies have shown that the cruciferous vegetable extract indole-3-carbinol (I3C) modulates estrogen hormones by favorably changing the ratio of protective 2-hydroxyestrone versus the damaging 16-hydroxyestrone.1 Indole-3-carbinol also induces phase I and II detoxifying enzymes that can help neutralize estrogen metabolites and xenobiotic estrogen-like environmental chemicals.2 Human studies support the beneficial role of I3C in positively altering estrogen metabolism.3 Di-indoyl-methane (DIM), a phytonutrient found in cruciferous vegetables, has been shown in animal studies to help maintain normal levels of a potentially damaging estrogen called 4-hydroxyestrone.
The glucosinolates are major constituents of cruciferous vegetables that have been shown to promote normal apoptosis and induce the expression of the beneficial gene via an estrogen-independent action.
Watercress contains isothiocyanates, but in a broader spectrum than does broccoli. The primary isothiocyanate precursor (PEiTC) in watercress functions via four specific mechanisms to maintain healthy cell division.6 Extracts from rosemary enhance liver metabolism of estradiol and estrone,7 inhibits the formation of DNA adducts,8 and have been shown to impede estrogen-induced growth promotion in certain tissues.
