Bone metastases have been reported to occur in half of all cancer patients whose cancer has spread to some other part of their body. That means nearly 250,000 people a year have bone metastases and suffer from their complications, which include fractures, pain, and spinal cord compression.

"It's very, very common in breast and prostate cancer and fairly common in lung cancer as well for [the cancer] to go to the bone, involving complications. Zoledronic acid is one of the few cancer drugs where you actually feel better when you're on it," says lead author James Berenson, MD, a professor of medicine at UCLA and director of Multiple Myeloma and Bone Metastasis Programs at Cedars-Sinai Medical Center in Los Angeles.

Berenson further explains that the current drug treatment, pamidronate, is given monthly, generally for the rest of a patient's life; therefore, cutting the treatment time from two hours to five minutes could have a significant impact.

Many cancers, such as breast cancer and multiple myeloma, usually appear in the bones as osteolytic lesions, which are areas where the bone becomes less dense than normal due to the action of osteoclasts (cells that break down bone tissue). However, prostate cancer and others more often cause osteoblastic lesions, which are denser than the surrounding bone. Other cancers present a "mixed" osteolytic and osteoblastic picture. This study did not look at effects of zoledronic acid on either osteoblastic or mixed lesions. Still, the experts say the results are encouraging.

Both zoledronic acid and pamidronate are part of a new class of drugs that slow down the action of osteoclasts. "The only treatment available [for bone metastases] before these drugs was radiation. But there's a limit to how much radiation therapy you can give. It has side effects," says Harmon Eyre, MD, chief medical officer at the American Cancer Society (ACS). Those side effects include fatigue and sleep disturbance. "What zoledronic acid does is take this treatment a step further. It's a much easier drug to give [than pamidronate] and appears to be equally well-tolerated and equally effective if you give the right dose."

In this multi-center study, 280 patients with bone lesions due to metastatic breast cancer or multiple myeloma (a type of blood cancer) received either zoledronic acid or pamidronate. The zoledronic acid was given in three different dosages, 0.4 mg, 2 mg or 4 mg. Pamidronate was given at a dose of 90 mg.

The main criteria used to judge the effectiveness of the drugs was the lack of a need for radiation therapy. Other variables such as bone fractures and patient pain levels were also factored in. After a 10-month study, all but the 0.4 mg dose of zoledronic acid were found to be effective.

This study was a prelude to larger Phase III trials that are currently underway. But Berenson says zoledronic acid will probably reach the market before those trials are even completed, as an approved treatment for hypercalcemia (abnormally high concentration of calcium in the blood) associated with malignancy. "I think the hypercalcemia malignancy approval, which has been done in many foreign countries, should be forthcoming in the U.S. pretty soon," says Berenson.

If that is the case, Eyre adds, doctors could use zoledronic acid "off label" to treat other problems, such as bone lesions.

"Metastatic cancer to bone is disabling. It's very painful," says Eyre. "Finding new drugs that give you better options is always important. And certainly the impact on the quality of life should not be underappreciated by anybody."