Researchers say the high rate of smoking among people with multiple sclerosis could be one reason for the elevated risk.

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Researchers say the risk of respiratory cancers in particular is high among people with multiple sclerosis. Getty Images

People with multiple sclerosis (MS) may have a greater risk for developing cancer than people in the general population, according to new research.

These findings were presented last week at the fifth European Academy of Neurology (EAN) Congress in Oslo, Norway.

“This study is the first to compare cancer risk in MS with non-affected siblings of MS patients. The risk assessment between these two groups is extremely interesting because they share the same genetics and environmental conditions,” Nina Grytten, PhD, postdoctoral researcher at the Western Norway Regional Health Authority and lead researcher, said in a press release.

The research was based on data from various Norwegian MS and cancer registries.

Included were 6,883 people with MS who were born between 1930 and 1979, as well as 8,918 siblings and 37,919 people without MS.

The overall cancer risk for people with MS was 14 percent higher than for people without MS, according to the study’s researchers.

They also reported the risk was especially high for certain cancers. The increase in risk was 66 percent for respiratory cancers, 52 percent for central nervous system cancers, and 51 percent for urinary cancers.

When compared with their siblings, however, people with MS didn’t have an overall higher risk for cancer. That’s because siblings of people with MS were found to have a higher risk for hematological cancers than people with MS and people in the general population.

Study authors acknowledge the increased cancer risk for people with MS may be due to excessive smoking and surveillance bias.

This was an observational study. Grytten cautioned that conclusions about causality can’t be made.

Dr. Jack Jacoub is a medical oncologist and medical director of MemorialCare Cancer Institute at Orange Coast Medical Center in California.

Jacoub told Healthline it’s important to keep in mind that the study took place in another country. That means demographic and environmental differences exist.

“When making population-based studies and comparing to another place, there are inherent variables impossible to control for. Nonetheless, they had a good number of patients, and the increased rates of cancer were unusually high,” he said.

According to the Cleveland Clinic Mellen Center for Multiple Sclerosis, smoking is common among people with MS.

Surveys indicate that 45 to 52 percent of people with MS are current or past smokers.

Smokers develop more autoimmune conditions and higher levels of co-morbidities. One of the most common co-morbidities for people with MS is chronic lung disease.

The study spanned 65 years, during which time smoking rates generally declined.

The Norwegian Institute of Public Health puts the smoking rate at 35 percent in 1990 versus 17 percent in 2013.

In the United States, cigarette smoking rates among adults fell from 43 percent in 1965 to 14 percent in 2017, according to the American Lung Association.

Jacoub explains that in MS, as well as other immune system disorders, the immune system shifts efforts from targeting infection and other invaders to targeting the body itself.

“The immune system, along with other factors, is usually able to control cancer cells and not allow them to form a tumor and create disease. If you have immune dysfunction, the ability to do that is not very effective,” Jacoub said.

Dr. Santosh Kesari is a neuro-oncologist and chair of the department of translational neurosciences and neurotherapeutics at the John Wayne Cancer Institute at Providence Saint John’s Health Center in California.

Kesari told Healthline the study highlights the role of inflammation in a variety of diseases, from autoimmune disorders such as MS to cancer.

“The paper suggests a genetic component to MS and abnormal immune system function in siblings, who may have that as well, even though they don’t have MS. Immune system dysfunction is predisposing to cancer, mainly hematological cancers,” Kesari said.

“The main thing is the connection between immune health and various disorders. Cancer, heart disease, brain function: We’re finding out the immune system is involved in dementia and other disorders of aging,” he added.

MS treatments may also play a role.

“MS patients, because they’re trying to control an overactive immune system, are on drugs that suppress the immune system, which increases the risk of developing cancer as well,” Kesari said.

Kesari notes people with MS tend to have more monitoring in general. Abnormalities that may turn out to be cancer are more likely to be found early.

That’s the surveillance bias the study authors mentioned.

There’s little difference in how people with MS are treated for cancer compared to people without MS.

“Typically, we don’t manage it differently as far as chemotherapy. For people with MS, sometimes chemo will even put MS in remission and control the disease for a long time,” Jacoub said.

“But there should be some hesitation and discussion when it comes to treating people with cancer and MS with immunotherapies due to the potential for adverse events,” he continued.

The study suggests that siblings of people with MS have an increased risk for developing blood cancers. According to Jacoub, this speaks to the immune system issue.

“There are familial links with autoimmune illness. This study is not enough to say siblings should seek extra screening. But doctors should be aware of the potential risk of some cancers if someone in the family has an autoimmune disease,” Jacoub said.

The National Multiple Sclerosis Society cautions that these finding should be considered preliminary.

The paper hasn’t yet been published in a peer-reviewed journal. Other large-population studies are needed to fully understand what it means for people with MS and their families.

“These studies offer hypotheses. They generate leads into more research and better understanding. Clear observation provides a powerful message,” Jacoub said.

“If accurate and this can be reproduced, guidelines may be changed so that patients who are asymptomatic are screened to try to catch cancer earlier,” he said.