SEATTLE—Patients with multiple sclerosis (MS) who take mitoxantrone have a significantly higher risk of leukemia than previously reported, according to research presented at the 61st Annual Meeting of the American Academy of Neurology. Vittorio Martinelli, MD, and colleagues found that acute leukemia occurred in 0.74% of patients with MS who took mitoxantrone, compared with prior studies that have reported leukemia rates ranging between 0.07% and 0.25% among those who had taken the drug.
Dr. Martinelli’s group included 2,854 Italian patients with MS who had been taking mitoxantrone since 1999 and observed them for at least one year. About 51% of patients had secondary progressive MS, 41% had relapsing-remitting MS, and 8% had primary progressive MS. Retrospective data were collected regarding total number of patients treated at each of the 35 MS centers in the study, cumulative dose of drug taken, and length of follow-up, noted Dr. Martinelli, who is a Head of the Department of Neurology and the Multiple Sclerosis Center at San Raffaele Institute in Milan.
Dr. Martinelli reported that 21 patients have developed acute leukemia thus far, and eight of these patients have died. The cumulative incidence of acute leukemia was 7.4 per 1,000, and the incidence rate was 0.16 per 1,000 person-months. Patients with acute leukemia had received a greater number of mitoxantrone administrations than did patients who did not have acute leukemia (8.6 treatment cycles vs 7.2, respectively), as well as a greater cumulative dose (82.4 vs 62.9 mg/m2, respectively).
Patients developed leukemia an average of 37 months after beginning mitoxantrone therapy and a mean of 18 months after the end of treatment. Using a cumulative dose of 82.4 mg/m2 or higher as an expositive factor, the researchers observed an incidence rate ratio of 2.74.
“The incidence of acute leukemia in Italian patients with MS treated with mitoxantrone is significantly higher than previously reported,” stated Dr. Martinelli. “The potential risk of acute leukemia should be carefully considered against the potential benefits of mitoxantrone treatment on every single patient.
“It is vital that all patients with MS treated with mitoxantrone undergo prolonged and careful hematologic follow-up to check for acute leukemia,” he concluded.
—Colby Stong