Drugs used to treat osteoporosis (bone loss) in women may be helpful for some men with metastatic (spread to bone) prostate cancer, according to a recent report.

Researchers found that zoledronic acid delayed bone fractures and improved prostate cancer tumors that had spread to the bone in some men. The study was reported in the Journal of the National Cancer Institute (Vol. 94: 1458-1468).

Despite its usefulness for some patients, zoledronic acid did not improve overall survival or slow the rate of tumor growth. The treatment did not slow the progression of pain, and quality of life was not improved, said Fred Saad, MD, and colleagues from Canada, the US, and Brazil, reporting for the Zoledronic Acid Prostate Cancer Study Group.

And some experts believe the overall benefits have not been proven and can only be recommended for those prostate cancer patients who are at high risk for bone fractures.

Bone weakness and fractures are a problem for men with advanced prostate cancer. These occur because of cancer spreading to the bone, osteoporosis, or even the hormone medicines used to treat the disease.

Zoledronic acid, also called Zometa, was recently approved by the Food and Drug Administration (FDA) for the treatment of cancer that has spread to the bone in multiple myeloma and solid tumors such as breast cancer and prostate cancer.

Zometa belongs to a group of drugs called bisphosphonates which are used to alleviate the pain and other complications associated with cancer that has spread to bones

The drug is given intravenously (IV) over a much shorter time per treatment (15 minutes compared to two hours) than another drug, pamidronate. But zoledronic acid is more expensive than pamidronate, experts point out.

In this study, researchers wanted to know whether these drugs could help prevent the spread of prostate cancer to the bone, decrease the size of prostate cancer tumors that may form in the bone, decrease the pain of prostate cancer in the bone, or extend survival.

They treated 643 men from 1998 to 2001 with one of three programs: a placebo (in this study it was an IV fluid that contained no medicine), a high dose (8 mg) of zoledronic acid, or a low dose (4 mg).

Men were selected for the study if they had evidence of prostate cancer spread to the bone. They could receive other cancer treatment while on zoledronic acid.

During the trial, the high dose treatment group had an increased number of men who developed kidney problems — a known side effect of the medication. As a result, their dose was reduced to 4 mg, and all the patients who were started on zoledronic acid treatment afterwards received the lower dose of the medicine.

The doctors found that the medicine did prevent bone problems to some degree in the men who received zoledronic acid compared with the group that was not given the medicine. The men who received the lower dose of the medicine actually did a bit better than the men who started out on the higher dose, and who had to have their medicine dose cut back.

It also took a longer time for men treated with zoledronic acid to develop their first evidence of a bone problem, such as a fracture, compared to the men on the placebo.

A small number of men (about 5%) in each group, including those receiving no medicine, had improvement in their prostate cancer tumors that had spread to the bone.

The researchers also noted that several other findings did not differ between the treatment groups. The treatment did not slow the progression of pain in the men treated with zoledronic acid. Quality of life was the same for all three groups.

The authors noted that zoledronic acid did decrease the risk of fractures in men with prostate cancer. Despite this, it did not improve overall survival or slow the rate of tumor progression.

There were side effects from the treatment. The most common ones included tiredness (fatigue), anemia, muscle discomfort, fever, and swelling of the legs. The kidney problems seen in the men receiving the 8 mg dose were resolved by decreasing the dose of the medicine to 4 mg, and by giving the zoledronic acid over 15 minutes instead of five minutes.

In an editorial in the same journal, Christina M. Canil, MD, and Ian F. Tannock, MD, PhD, both from the Princess Margaret Hospital in Toronto, Canada reviewed the evidence about the use of bisphosphonate drugs in men with prostate cancer.

Canil and Tannock had reservations about the broad meaning of the research. They concluded, "This study with zoledronic acid has not provided a clear demonstration of net therapeutic benefit."

"The study by Saad … adds to the evidence that bisphosphonates have some activity in reducing the incidence of skeletal related events in men with metastatic prostate cancer but with some added toxicity," wrote Canil and Tannock.

"Zoledronic acid is a reasonable option for patients who do not respond to alternative therapies and who are at high risk for bone fractures or spinal cord compression," they said.

But they also cautioned, "Currently zoledronic acid cannot be recommended as a standard therapy for men with prostate cancer and metastases to bone."

Saad and his colleagues said their findings showed that zoledronic acid was beneficial for some patients with metastatic prostate cancer, and they recommended additional studies to find out if starting the medicine earlier in the course of disease would improve the results.