Hundreds of very common chemicals found to increase breast cancer risk

Hundreds of chemicals found in everyday products may increase one's risk of developing breast cancer, according to a new study. These chemicals impact breast cancer risk by causing breast tissue cells to secrete more of the hormones that can lead to breast cancer, the researchers explain, though how they cause this change isn't clear.

The new research comes from the Silent Spring Institute, which pulled data on chemicals from the EPA's ToxCast program, finding that out of more than 2,000 substances, 296 could increase either estrogen or progesterone hormone levels in breast tissue cells. Of these 296 chemicals, 71 increased the levels of both hormones.

The study notes that these chemicals can be readily encountered on a frequent basis in everything from hair dye to pesticides and some of the flame retardants used on furniture. The researchers note that women are likely to be exposed to some of these chemicals every day, often from multiple sources.

Of particular concern, the researchers say, are the chemicals that are able to increase progesterone levels in these cells — the same hormone that was linked to increased breast cancer risk from hormone replacement therapy. The link between elevated levels of these hormones and the often deadly cancer is well established.

Back in 2002, a study from the Women's Health Initiative found that combo hormone replacement therapies — the kind that featured both estrogen and progesterone — were linked to increased breast cancer risk. Underscoring the finding, the rates of breast cancer decreased as the rate of combination hormone therapy use decreased.

Unfortunately, safety tests on chemicals often fail to include their potential impact on hormone level changes in mammary glands following exposure to the substance. The institute points to this new study as a "wakeup call" for regulators to ensure chemicals are tested for safety — and that includes potential breast cancer risk.