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Combined Analysis of Two Pamidronate Trials Shows Treatment Failed To Relieve Bone Pain, Prevent Fractures
In about eight out of 10 men with advanced prostate cancer, the disease spreads (metastasizes) to the bones, causing pain and increasing risk for fractures and spinal cord compression.
Bisphosphonates are a class of drugs that inhibit bone breakdown. Previous studies have shown that these drugs are helpful in the treatment of bone metastases of breast cancer and multiple myeloma and that they can reduce bone breakdown in patients with advanced prostate cancer.
Other studies showed that pamidronate, a member of the bisphosphonate family, stemmed loss of bone density in men receiving hormonal therapy for prostate cancer. In general, loss of bone density increases an individual's risk of fracturing a bone. However, these studies did not offer any direct evidence that pamidronate prevented fractures in patients with prostate cancer.
The current study combines the findings of two phase III clinical trials, one performed in the United States and one in several other countries. The study's principal author is Eric J. Small, M.D., of the University of California, San Francisco, Comprehensive Cancer Center.
The two trials involved a total of 378 patients with prostate cancer that had spread to the bones after becoming resistant to hormonal therapy. Patients were randomly assigned to receive either pamidronate or a placebo by intravenous infusion every three weeks for 27 weeks. Both trials were double-blinded - that is, neither the patients nor their doctors knew who was getting the drug and who was getting the placebo until the study's end.
In both studies the main objective was to find out if pamidronate reduced patients' pain or use of pain-killing medication. At each treatment session, patients filled out a scale that rated their pain from 0 (no pain) to 10 (worst pain imaginable).
In addition, patients were asked to record how much pain-killing medication they took every day. Doctors also tracked how many patients suffered a bone complication such as a fracture, received radiation therapy to treat bone pain, or underwent surgery or radiation therapy to treat or prevent a fracture.
Regardless of whether patients received pamidronate or a placebo, their pain scores were not significantly different at 9 weeks or at 27 weeks of treatment than they had been at the beginning of the study.
In a subset of patients whose use of pain-killing medications either declined or remained stable during the study, average pain scores at 9 weeks declined more among patients taking pamidronate than among those taking a placebo, but the difference was small and disappeared by 27 weeks.
On the basis of these findings, pamidronate cannot be recommended for patients with bone metastases of advanced prostate cancer, says William Dahut, M.D., chief of the National Cancer Institute's Genitourinary Clinical Research Section at the National Institutes of Health Clinical Center in Bethesda, Maryland.
Dahut thinks it would be reasonable, however, for doctors to recommend that these patients consider taking another bisphosphonate, zoledronic acid (also called zolendronate, brand name Zometa®). In a study published in 2002 (see a summary), zoledronic acid did reduce fractures and other bone complications in men with prostate cancer that had spread to the bones.
Both patients and their doctors should keep in mind that zoledronic acid may cause side effects such as fever, nausea, and changes in kidney function, Dahut adds. In addition, although the drug appears to reduce bone complications, there is no evidence that it significantly reduces bone pain or extends patients' survival.
Source: The National Cancer Institute