SAN FRANCISCO — Zoledronic acid therapy increased bone mineral density in men with nonmetastatic prostate cancer even when started more than a year after initiation of androgen deprivation therapy, Dr. William R. Broderick reported at a symposium on genitourinary cancers.
The double-blind study included 93 men with nonmetastatic prostate cancer who were initiating or already on androgen deprivation therapy (ADT). The patients were randomized to receive four courses of 4 mg IV of the bisphosphonate zoledronic acid at 3-month intervals or intravenous placebo therapy on the same schedule. All patients had bone mineral density T scores at or below −2.0 at baseline. Their bone densities in the lumbar spine, hips, and femoral necks were checked at 6 and 12 months by dual-energy x-ray absorptiometry (DXA) scans.
Among 50 men who had been on ADT for less than 1 year, spinal bone mineral density increased by 6% in the 26 randomized to zoledronic acid therapy and decreased by 3% in 24 men randomized to placebo. Among 43 men who had been on ADT for 1 year or longer, spinal bone mineral density increased by 6% in the 22 randomized to zoledronic acid therapy and by 2% in 21 men randomized to placebo, Dr. Broderick said at the symposium, which was sponsored by the American Society of Clinical Oncology, the American Society for Therapeutic Radiology and Oncology, and the Society of Urologic Oncology.
Spine density results differed significantly between the zoledronic acid and placebo groups, but did not between patients stratified by their amount of time on ADT, said Dr. Broderick of the Veterans Affairs Hospital in Hines, Ill., and of Loyola University Chicago, Maywood.
The study was funded by Novartis, which markets zoledronic acid as Zometa.
Androgen deprivation therapy for prostate cancer has been associated with increased risks for osteoporosis and fracture. Previous studies have shown that initiating bisphosphonate therapy when starting ADT can delay the development of osteopenia or osteoporosis, but no studies have looked at starting bisphosphonate therapy in these patients after they've been on androgen deprivation therapy for more than a year.
“It makes sense conceptually, but we never had the data to show it. Now we do,” Dr. Broderick said at his poster session. The current results also suggest that “perhaps we don't need to start bisphosphonate therapy up front in everyone,” which could save some expense and avoid side effects, he added. “Perhaps we can delay bisphosphonate therapy in these patients until we are starting to see that they are becoming osteopenic.”
The study was not designed to identify the best timing for starting bisphosphonate therapy in men on ADT, “but it does give us evidence that zoledronic acid works if we do start it at a later point in time” than usual, he said.
All the men in the study were started on 1,000 mg/day of supplemental calcium, 400 IU/day of vitamin D, counseling, weight-bearing exercise, and smoking cessation programs (if applicable). Demographics and other characteristics were similar between the group on androgen deprivation therapy for less than 1 year and the group with 1 or more years of ADT, except that those on ADT were significantly older—72 years, compared with 69 years.