FRIDAY, Feb. 4 (HealthDay News) -- Middle-aged breast cancer survivors face an increased risk for hip fractures, a condition normally uncommon in women younger than 70, a new study has found.

Researchers at Northwestern University in Chicago say that this may be because early menopause caused by breast cancer treatment and the effects of breast cancer drugs could weaken the bones by the time women reach middle age.

The finding came from a study of six women who had survived breast cancer and, in their early 50s, were being treated for hip fractures.

Most of the women did not have osteoporosis, but they did have lower-than-normal bone mineral density (osteopenia). This suggests that rapid changes in bone architecture caused by chemotherapy, early menopause and adjuvant breast cancer therapy may not be detected on a bone mineral density test, said Dr. Beatrice Edwards, an associate professor of medicine and orthopedic surgery and director of the bone health and osteoporosis program Northwestern University's Feinberg School of Medicine, who led the research.

The women had been diagnosed with early-stage breast cancer, and their treatments had included lumpectomy, radiation therapy and chemotherapy with cytoxan and adriamycin for one to four years before they broke a hip. All of the women were perimenopausal at the time of the fracture.

In four of the women, their breast cancer had grown in response to estrogen, and their cancer therapy had included aromatase inhibitors to prevent their bodies from making estrogen. Recent research has linked aromatase inhibitors with possible bone loss in women.

"Although the majority of women with breast cancer can expect to be fully cured from the disease, the prevention of cancer treatment-induced bone loss is important to consider in cancer survival," Edwards said in a university news release.

"More research needs to be done before treatment guidelines are changed, but greater awareness of the adverse effects of certain breast cancer drugs is needed," she added.

The study is in the February issue of Clinical Cancer Research.

More information

The American Academy of Orthopaedic Surgeons has more about hip fractures.