Mitoxantrone, a drug used to treat multiple sclerosis (MS), may increase the risk of colorectal cancer, according to an article published in Neurology.

Mitoxantrone is a topoisomerase II inhibitor indicated for the reduction of neurologic disability and/or frequency of clinical relapses in secondary (chronic) progressive, progressive relapsing, or worsening relapsing-remitting MS; it is not indicated for the treatment of primary progressive MS. Previous studies, which have shown an increased risk of leukemia and heart damage, have limited the use of mitoxantrone.

For this study (n=676), a team of German researchers investigated whether mitoxantrone increased the risk of other types of cancer. They evaluated patients with MS treated with mitoxantrone from 1994–2007 and followed up until 2010. 

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Of the total patients, 5.5% (n=37) were diagnosed with cancer: 9 patients with breast cancer, 7 with colorectal cancer, and 4 with acute myeloid leukemia. The rate of leukemia in particular, was 10 times greater in patients treated with mitoxantrone than the general population in Germany. The rate of colorectal cancer was 3 times greater compared to the general population. Study authors found no greater likelihood of developing breast cancer and all other types of cancer in patients who took mitoxantrone vs. the general population.

Older age at the start of mitoxantrone therapy was the only factor associated with a higher risk of cancer.

Mathias Buttman, MD, author of the study, concluded, “Mitoxantrone is the only approved treatment for people with secondary progressive MS without relapses and should be considered in people where the disease is evolving quickly.” Though an increased risk of leukemia and colorectal cancer was seen, the overall rate is small enough to justify use of mitoxantrone in patients severely affected by MS, he concluded. If the results from this study are confirmed, Dr. Buttman said colonoscopies should be performed after treatment to screen for colorectal cancer.

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