Bone Drug May Prevent Return of Breast Cancer

June 3, 2011 -- A drug that battles bone loss may have added benefits for women with estrogen-sensitive breast cancers, significantly reducing the chance that their cancer will return or spread, a new study shows.

What's more, researchers say, the lowered risk of recurrence seems to last years after the treatment, a bisphosphonate drug called Zometa, is stopped.

"I find that very reassuring. It obviously demonstrates that we can impact on the long-term outcome of our patients with an early intervention. We do not have to give these drugs forever. I'm very enthusiastic about this," says study researcher Michael Gnant, MD, professor of surgery at the Medical University of Vienna in Austria.

For the study, which is published in TheLancet, 1,803 premenopausal women with early-stage, estrogen-driven breast cancers were given a drug which suppresses estrogen production by the ovaries. They were also treated with drugs, Arimidex or tamoxifen, that help prevent cancers from using estrogen to grow.

In addition to those treatments, half were randomly assigned to receive intravenous infusions of Zometa every six months for three years.

Two years after their treatments ended, women who got the bone drug continued to have a 32% reduced risk of cancer recurrence compared to those on estrogen suppression alone.

Overall, 92% in the Zometa group were cancer-free two years after treatment compared to 88% on estrogen suppression alone.

How Bone Drugs May Stifle Cancer

Tumors can shed cells that migrate to the bone marrow, where they may hide and be protected from cancer-killing drugs.

One theory is that these wandering tumor cells appear to stimulate the activity of osteoclasts, or cells that break down bone.

The activity of osteoclasts, in turn, appears to further spur these castoff tumor cells, a synergy that can reignite the cancer and cause it to return or spread.

It's thought that bisphosphonates like Zometa put the brakes on this cycle by slowing the activity of osteoclasts, which then quiets the rogue cancer cells.

"There is kind of an expiry [expiration] date to these dormant tumor cells," Gnant says. "You don't have to use all these treatments forever. If you manage to get the right window, then basically you can eradicate them and this would eventually mean a cure for our patients, which is obviously a word we should only use very humbly."

Conflicting Findings

A large British trial presented in December at the San Antonio Breast Cancer Symposium found that Zometa treatment did not reduce the risk of recurrence in women with early-stage breast cancers.

Not all of the women in that study received estrogen-suppressing therapy, however, and experts say that may be a key difference.

A subset of women in that study, those who had been postmenopausal for at least five years and thus had naturally lower estrogen levels, did see some survival benefit after taking Zometa compared to those on conventional therapies alone.