THURSDAY, June 24 (HealthDay News) -- Bone-building drugs known
as bisphosphonates appear to reduce the risk of invasive breast
cancer by around 30 percent, two new studies show.
"If a woman is considering bisphosphonate use for bone, this might be another potential benefit," said Dr. Rowan T. Chlebowski, a clinical oncologist at the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, Calif. He is the lead author of one of the two studies on the topic, published online this week in the Journal of Clinical Oncology.
The findings were first presented late last year at the San
Antonio Breast Cancer Symposium, but Chlebowski said the results
now have the benefit of having been peer-reviewed before
publication for scientific accuracy.
Chlebowski and his colleagues looked at nearly 155,000 women who
participated in the Women's Health Initiative (WHI) study,
evaluating the 2,816 women who took oral bisphosphonates at the
study start and comparing them to women who did not.
Ninety percent of the women who were taking the bone-building
drugs took alendronate (Fosamax), according to the study.
After nearly eight years of follow-up, Chlebowski found invasive
breast cancer incidence was 32 percent lower in those on
bone-building drugs, with ER-positive cancers reduced by 30
percent. The incidence of ER-negative cancers in those on
bisphosphonates also decreased, but not by enough to be
The incidence of early, noninvasive breast cancers, known as
ductal carcinoma in situ, was 42 percent higher in bisphosphonate
users, so the bisphosphonates could somehow be selectively
affecting invasive cancers, Chlebowski postulated.
In a second study, conducted in Israel, researchers looked at
4,039 postmenopausal women, including some who took bisphosphonates
and some who did not. Those who took the drug longer than a year
had a 39 percent reduced risk of breast cancer; after adjusting for
factors such as age and family history, there was still a risk
reduction of 28 percent.
Exactly how the drugs reduce risk isn't known. Chlebowski
speculated that the drugs may block the release of growth factors
that would encourage tumors to grow or may block blood vessel
formation within a tumor.
It's known that low bone mineral density (BMD) is linked with a
reduced risk of breast cancer, and women with low BMD are likely to
be on the drugs. So for the study analysis, Chlebowski adjusted for
this possible confounding effect by incorporating a hip fracture
risk score to take into account the bone mineral differences
between drug users and non-users.
Another expert, Dr. Joanne Mortimer, director of the women's
cancers program at the City of Hope Comprehensive Cancer Center in
Duarte, Calif., pointed out that the studies found an associative
link, not a cause-and-effect, so it's not definitive.
However, she said, "for people with osteoporosis, it's one more
reason to feel comfortable taking a bisphosphonate."
Like other medications, the drugs have favorable and unfavorable
effects. For instance, researchers recently found women on the
bone-building drugs can have a higher risk of an uncommon fracture;
that research is being evaluated further, Mortimer said.
>From the two studies, however, Mortimer said, it appears
that "these drugs change the environment in such a way that cancer
cells are less likely to take root and grow, not only in the bone
marrow but elsewhere as well."
In an accompanying editorial, Dr. Michael Gnant, of the Medical
University of Vienna, said future studies will help pinpoint the
benefit of the drugs in breast cancer incidence reduction and
supply more answers as to their best use.
Chlebowski reported that he has been a consultant to Novartis
and Amgen, which make the bone-building medications.
To learn more about osteoporosis, visit the
National Osteoporosis Foundation.