NEW YORK--The vinca alkaloid vinorelbine tartrate(Drug information on vinorelbine tartrate) (Navelbine) has demonstrated clinical efficacy in hormone refractory prostate cancer as measured by time to disease progression, performance status, and pain indices, as well as bone scans and PSA analysis, Howard A. Burris, III, MD, told Oncology News International.
"One of the problems in dealing with prostate cancer is that we traditionally evaluate drugs by looking at an objective response rate. But in prostate cancer, the paucity of patients with measurable disease has prevented this as an endpoint," said Dr. Burris, director of clinical research at the Cancer Therapy and Research Center and director of drug development at Brooke Army Medical Center, San Antonio.
With chemotherapy producing a steady 10% to 20% response rate, the focus tends to shift to palliative advantages. Though these endpoints need to be validated, they do appear to be useful for evaluating new drugs for hormone refractory prostate cancer, Dr. Burris said.
In the San Antonio trial, the vinorelbine schedule was 22 mg/m² IV, weekly for 8 weeks, and then repeated every other week. The 20 patients enrolled averaged more than five cycles or 5 months of therapy--"a good prognostic sign," Dr. Burris said. Patients experienced only mild toxicities and brief neutropenia.
A positive response was defined as a greater than 25% change from baseline in one endpoint. By this measure, six of the 20 patients were positive responders, producing a clinical benefit rate of 30%--33%, if two patients who discontinued for personal reasons were not included. Dr. Burris earlier reported these findings at the Chemotherapy Foundation Symposium XII, sponsored by Mount Sinai School of Medicine.
The Texas researchers were also encouraged by the fact that nine other patients experienced stable disease while only three had truly progressive disease.
All six responders had improvement in Karnofsky status and pain indices, and three were able to discontinue analgesics entirely. The range of PSA reductions was wide, between 3 and 80 ng/mL, probably because some patients enrolled with relatively low PSA scores, he said.