The Link Between Breast Cancer and Osteoporosis

Powerful chemotherapy drugs and estrogen-blocking hormone treatments are highly effective in treating breast cancer. But in the process they may be putting women at risk of another disease: osteoporosis.

Women with breast cancer may face a greater risk of developing osteoporosis. The two conditions both affect post-menopausal women, making age and gender strong risk factors. Researchers are finding that some drugs used to treat breast cancer may have an effect on bone mineral density as well, potentially increasing the risk of bone loss in these women.

"Osteoporosis is a common problem. Women with breast cancer may be particularly at risk. This is because certain treatments for breast cancer may promote bone loss. These women should pay attention to nutrition and exercise and should consult with their physician," says Catherine Van Poznak, M.D., a breast oncologist at the University of Michigan Comprehensive Cancer Center.

Van Poznak and others are conducting research into how best to manage breast cancer and maintain bone health. One trial at the U-M Comprehensive Cancer Center explores the effects chemotherapy has on bone mineral density in postmenopausal women. The researchers hope to identify which women are at increased risk for losing bone mass and which women would benefit from drugs designed to stop bone loss.

It's not known how chemotherapy works against bone health. It could be that because chemotherapy affects cells that divide quickly, it might alter bone mass. Another class of drugs, called aromatase inhibitors, block the production of estrogen, making them an effective treatment for certain types of breast cancer. While lowering estrogen levels is beneficial in fighting breast cancer that is fueled by hormones, it is harmful to bone health since estrogen helps bones stay strong.

For premenopausal women treated for breast cancer, osteoporosis is also a concern. In addition to the possible effect of chemotherapy on bones, the cancer treatment may induce early menopause, putting this group at a similar risk as older women in menopause.

Osteoporosis is a condition that thins and weakens the bones to the point where they break easily. Some 44 million Americans, primarily women, have osteoporosis. About 214,600 women will be diagnosed with breast cancer this year.

Certain drugs used to treat breast cancer may help prevent osteoporosis. The drug tamoxifen is used to prevent estrogen from fueling cancer cell growth. But because it is not stopping the body's production of estrogen like aromatase inhibitors, tamoxifen has been shown to increase bone density in postmenopausal women. Tamoxifen is used by women who have been diagnosed with breast cancer as well as women at high risk for the disease. In addition, the drug raloxifene, which is used to treat osteoporosis, was recently found to be effective in preventing breast cancer in women at high risk.