A new study has found that an osteoporosis drug protects against the bone damaging side effects of certain breast cancer medications. Published early online in Cancer, a peer-reviewed journal of the American Cancer Society, the study indicates that some breast cancer patients could take zoledronic acid in addition to their anti-cancer medications to maintain bone health.
Drugs called aromatase inhibitors stop the production of estrogen in postmenopausal women and therefore make less estrogen available to stimulate the growth of certain breast cancer cells. Many postmenopausal women with breast cancer are routinely treated for several years with these potentially life-saving drugs, but the agents can cause bone loss and fractures.
Adam Brufsky, MD, PhD, of the University of Pittsburgh Cancer Institute, and his colleagues conducted a study to see if the bone drug zoledronic acid could prevent and treat bone loss in postmenopausal breast cancer patients. In their five-year study, called Z-FAST, 602 postmenopausal women with early breast cancer who were receiving the aromatase inhibitor letrozole were randomized to receive zoledronic acid simultaneously with letrozole or only after bone loss or fractures occurred.
The investigators observed significant and progressive increases in bone density throughout the five years of the study in women who initiated zoledronic acid at the start; in contrast, significant decreases in bone density occurred when zoledronic acid administration was delayed until bone loss was apparent. Over time, though, the rate of bone density decline in the delayed group slowed, most likely because more delayed patients received zoledronic acid by the end of the study. These findings indicate that bone density is maintained more effectively with upfront zoledronic acid, but bone loss is likely reversible so that initiating zoledronic acid, even after bone loss has developed, is beneficial.
Osteoporosis is a growing concern among breast cancer survivors and their doctors, because certain cancer drugs can cause bone loss.
But a new study has found that cancer drugs aren’t the only culprits. Among 64 breast cancer patients referred to a bone health clinic, 78 percent had at least one other cause of bone loss, including vitamin D deficiency, excessive calcium excretion in urine and an overactive parathyroid gland.
“Doctors evaluating breast cancer patients for possible bone loss should look further than cancer drugs,” said Dr. Pauline Camacho, lead author of the study in the Journal of Clinical Oncology. Camacho is an associate professor in the department of medicine, division of endocrinology and metabolism, Loyola University Chicago Stritch School of Medicine.
A co-author of the study, Dr. Kathy Albain, said breast cancer survivors “are just like the normal population as they age in that bone loss can be due to many treatable causes.” Albain is a professor in the Department of Medicine, division of hematology/oncology at Stritch.
Previous studies have found that chemotherapy drugs can cause bone loss. Studies also have found that a class of breast cancer drugs called aromatase inhibitors can decrease bone mineral density and increase the risk of fractures in postmenopausal women. Aromatase inhibitors decrease the body’s production of estrogen. While estrogen feeds cancer, it also protects against osteoporosis. Aromatase inhibitors include letrozole (trade name, Femara), anastrazole (Arimidex) and exemestane (Aromasin).
Loyola University Health System
“This study shows that bone loss from aromatase inhibitors can be prevented long term with a safe and effective drug that prevents osteoporosis,” said Dr. Brufsky. Zoledronic acid is currently approved by the U.S. Food and Drug Administration for conditions including osteoporosis and bone complications of cancer.
Breast Cancer Treatment and Bone Loss
Certain breast cancer treatments can speed up bone loss or cause you to lose more bone than you normally would:
Chemotherapy: Some chemotherapy medicines can have a direct effect on your bone health. In other situations, some women who are close to menopause and get chemotherapy may have significant bone loss because the chemotherapy causes early menopause. If chemotherapy pushes your body into menopause, bone loss may begin while you’re still having treatment and continue after treatment is done.
Aromatase inhibitors (a type of hormonal therapy):
* Arimidex (chemical name: anastrozole)
* Aromasin (chemical name: exemestane)
* Femara (chemical name: letrozole)
Aromatase inhibitors work by preventing the formation of estrogen. The loss of estrogen can lead to bone loss during treatment. Aromatase inhibitors are used most often in post-menopausal women diagnosed with hormone-receptor-positive early breast cancer.