Relative Cancer Risk is Higher in MS Patients Who Switch Disease-modifying Treatments More Frequently, Study Finds

The relative risk of developing cancer was found to be higher in multiple sclerosis (MS) patients who more frequently switched between disease-modifying treatments, according to a study.

In addition, researchers found an increased incidence of cancer in male MS patients from 20 to 50 years old, and in female MS patients over 50.

The data were reported in the study “Cancer Risk and Multiple Sclerosis: Evidence From a Large Italian Cohort,” published in the journal Frontiers in Neurology.

Previous research has discovered that MS and cancer may share some abnormal functions of the immune system.

To better understand the incidence of cancer in MS patients, and evaluate the impact of disease-modifying treatments (DMTs) on cancer risk, a team led by researchers at the University of Catania, Italy, compared a database of MS patients between 2003 and 2013 in Catania (the second largest city of Sicily in Italy) with the Integrated Cancer Registry of Catania-Messina-Siracusae-Enna, which collects information about cancer in the general population of that particular geographic area.

During the time period analyzed (2003–2013), 2,730 people were diagnosed with MS. Of these, 1,180 patients satisfied the inclusion criteria and were enrolled in the study (67.1% females; mean age of 41.2 years), and of those, a total of 36 incidences of cancer were observed.

Investigators then analyzed the number of cancer cases according to the “expected” number of cases in the Catania community based on the Integrated Cancer registry. These are the “standardized incidence ratios,” or SIR.

If the observed number of cancer cases in MS patients equals the expected number, the SIR is 1, meaning no increased cancer risk. If more cases are observed than expected, the SIR is greater than 1, meaning increased risk. If fewer cases are observed than expected, the SIR is less than 1, meaning less risk.

The results showed that the cancer risk was not significantly increased in the MS population as a whole (SIR of 1.18). However, when the analysis was focused on specific population subgroups, stratified based on age and gender, men between 20 and 50 years old (SIR of 2.84), and women over 50 (SIR of 1.82) showed a significantly higher risk of developing cancer.

These results suggested that some MS subpopulations may be more susceptible to developing cancer.

The team also investigated the effects of different MS treatment strategies on the relative risk (RR) of developing cancer. MS patients were divided into four subgroups: patients not treated with any disease-modifying treatment (DMT), treated with one DMT (“no switch”), treated with two DMT (“one switch”), and treated with more than two DMTs.

The RR of developing cancer was not significantly higher in the “no DMT” group, and slightly increased in the “no switch” group, but it was 1.99 (nearly two times higher) in the “one switch” group, and 3.38 (more than three times higher) in the group who switched at least twice.

Based on the results, the team hypothesized that “MS patients experiencing therapeutic failure with different immunomodulating and/or IS (immunosuppressive) [agents] could have an enhanced risk of cancer, because being exposed to different molecules with different mechanisms of action may negatively influence the innate and adaptive immune systems and make these patients more sensitive [to] carcinogenesis [cancer formation].”

In terms of cancer types, a significantly higher incidence of genitourinary and thyroid cancers was observed.

Additional analysis showed that age, age at MS onset, disease duration, and more that two DMT switches were associated with a higher risk of developing cancer.

“Our results demonstrated that cancer risk was not increased in our MS population; but age and sex different distribution may partly drive cancer risk. Higher cancer risk in MS patients switching more than two DMTs should [be] take[n] into account in treatment decision making,” the team concluded.