Radiation therapy to the chest before you were 30 years old: If you had radiation therapy to your chest before you were 30 years old and particularly during adolescence, you may have a higher risk of developing breast cancer. This has been seen in young women receiving radiation to treat Hodgkin's disease. (This does NOT include radiation therapy to treat breast cancer.)

Breast density: Past research has shown that women with “dense” breasts, which contain more glandular and connective tissue, are more likely to be diagnosed with breast cancer than women whose breasts are less dense (mainly made up of fat tissue). Breast cancer itself is dense and starts from glandular tissue. Estrogen makes breast tissue more dense. So the connection between breast density and breast cancer may be related to higher levels of estrogen in the body. On a mammogram, a cancer is harder to spot in dense tissue than in fatty tissue. That's because the cancer looks a lot like the glandular tissue around it.

Exposure to DES (diethylstilbestrol): DES is an estrogen-like hormone used in the past to help women prevent miscarriage. Daughters of women who used DES have an increased risk of cancer of the vagina. This drug may also increase the risk of breast cancer in women who used it and in their daughters who were also exposed to it.

Late pregnancy or no pregnancy: Women who had their first full-term pregnancy after age 30 and women who never had a full-term pregnancy are at higher risk for breast cancer than those who gave birth earlier in life. A full-term pregnancy, which stops your menstrual cycle for nine months, seems to offer protection against breast cancer.

If you weigh uncontrollable factors against those that CAN be changed, you'll see that you can do a lot to lower your risk of breast cancer. And while it's very hard to pin down specific foods or chemicals that are firmly linked to a higher or lower risk of breast cancer, researchers are working hard to find out whatever they can about specific lifestyle and environmental factors that may be within your control.