Overall, the incidence of cancer in the MS cohort ranged from 23.09 per 10,000 person-years for rituximab ever-takers to 46.28 for those who had ever taken fingolimod. Among the general population, rates of any malignancy were 29.62 per 10,000 person-years.
Breast cancer rates in the MS cohort ranged from 2.19 to 2.92/10,000 person-years. For the general population, the rate was 12.07/10,000 person-years.
Using a Cox regression analysis employing MS-specific covariates and using rituximab as the reference, Mr. Alping and his colleagues calculated an inverse proportion-weighted HR for any malignancy under the various treatment conditions.
Among women taking rituximab, 2,274 therapy starts occurred, and one breast cancer was seen in 4,050 person-years. This yielded an incidence of 2.32 cancers per 10,000 person-years (95% CI, 0.06–12.9). This contrasts with the adjusted incidence rate in the general female population of 11.06 breast cancers per 10,000 person-years.
Looking at all the therapy episodes captured in the cohort study, there were 6,660 incidences of therapy initiation, and 52 malignancies were seen over 17,283 person-years, Mr. Alping said.
No Increased Risk When Compared With the General Population
“For malignant cancer of any type, we found no increased risk for rituximab, compared with fingolimod and natalizumab,” Mr. Alping said, noting the wide confidence intervals in the adjusted data. The incidence of breast cancer in women who have taken rituximab is “comparable to, or possibly lower than, that of the general female population, and lower than the incidence rate reported in the ORATORIO trial for ocrelizumab,” he said. “The overall cancer risk and risk of breast cancer might not be major concerns in the short term when treating MS patients with rituximab, relative to other disease-modifying therapies,” Mr. Alping concluded.
The study was partially funded by the Patient-Centered Outcomes Research Institute.
—Kari Oakes