CHICAGO – Women taking zoledronic acid monthly for metastatic breast cancer that has spread to the bone may be able to get by with quarterly injections after a year of standard treatment.
The first phase III trial to compare the two dosing schedules for the bisphosphonate found that less frequent therapy produced "noninferior" outcomes compared with the current standard of care, Dr. Carla Ripamonti reported at the annual meeting of the American Society of Clinical Oncology.
Zoledronic acid (Zometa) has been shown to reduce skeletal-related events for up to 2 years in such patients, and international guidelines recommend its use until they experience a substantial decrease in performance status, said Dr. Ripamonti of the National Cancer Institute in Milan, Italy. The thinking behind the current trial was that after a year of treatment, a more convenient regimen "might contribute to improved patient compliance and safety, and help reduce cost while maintaining the efficacy of the drug."
Underscoring the universality of the issue, the invited discussant, Dr. Thomas J. Smith, director of palliative medicine at Johns Hopkins University’s Sidney Kimmel Cancer Center in Baltimore, introduced his comments with the observation, "I’m a breast cancer doctor, and so I see so many people who ask, ‘Do I have to come in every month for my zoledronic acid?’ And the answer is, ‘I don’t know.’ "
Dr. Ripamonti and her coinvestigators randomized 209 women to 4 mg of zoledronic acid every 12 weeks and 216 women to 4 mg every 4 weeks in the 12-month, open-label, multicenter ZOOM trial. All participants had received 9-12 infusions prior to entering the prospective study.
At the trial’s end, 149 and 142 women, respectively, had completed treatment with no difference in the skeletal morbidity rate, the primary end point, in an intent-to-treat analysis. The mean of the ratio of skeletal events per year to time on trial was 0.26 with quarterly treatment and 0.22 with monthly dosing, she reported.
The proportion of patients with skeletal-related events, a secondary end point, also was similar at 14.8% in the quarterly group and 15.3% in the monthly group.
Both schedules were well tolerated, with little difference in adverse events, she reported. The rate of renal side effects was 4% in each arm; osteonecrosis of the jaw occurred in 4 patients on the quarterly schedule and 3 treated monthly.
An assessment of median NTx (N-telopeptides of type I collagen) levels at baseline and every 3 months on study raised some concern, in that the bone resorption marker was increased at 6 months and stayed elevated in the quarterly group, but it did not rise with standard care. This suggests that "caution is needed and longer follow-up is needed to assess whether zoledronic acid every 3 months can maintain adequate efficacy in skeletal-related events over time," said Dr. Ripamonti.
Despite the generally positive results, she noted that the trial was conducted in just one country as an open-label study, it did not have a prespecified imaging frequency, and patients were followed for only 1 year. She urged clinicians to wait for data from the double-blind, phase III Optimize-2 trial, which compared the same dose schedules. Results will be available in the next year, and then oncologists "can decide how to change our clinical practice," she said.
Dr. Smith agreed. It’s "too early" to use NTx levels, he said, recommending that clinicians wait for new data and guidelines. If quarterly dosing becomes possible, he predicted the "cost will be one-third of what it was before."
"So don’t change your current approach, but stay tuned," he told attendees.
Dr. Ripamonti said she had no relevant disclosures. Dr. Smith said he received research funds from the American Cancer Society.