Multiple sclerosis associated with lower cancer risk overall

A new study shows that people with multiple sclerosis may be at a lower risk for cancer overall, but at a higher risk of developing certain types of cancer, such as brain tumors and bladder cancer.

The study is published in the March 31, 2009, print issue of Neurology, the medical journal of the American Academy of Neurology.

Researchers looked at the medical records of 20,000 people with multiple sclerosis and 204,000 people without the diagnosis. After 35 years, they found that the people with MS had a decreased overall risk of cancer by 10 percent compared to people who did not have the disease. The result was more pronounced in women. However, for people with MS the risk for certain cancers, such as brain tumors and bladder and other urinary organ cancers, increased by up to 44 percent compared to people without MS.

Scientists also evaluated the parents of people with MS to determine whether there was a possible genetic link. They found that there was no overall increased or decreased risk of cancer among either mothers or fathers of those with MS, compared to parents of people without MS.

"We speculate that the lower risk for cancer among people with MS could be a result of lifestyle changes or treatment following diagnosis," said study author Shahram Bahmanyar, MD, PhD, of the Karolinska Institute in Sweden. "The increase in brain tumor diagnoses may be due to brain inflammation, but this finding may not reflect a real increase in cancer risk, as there is some evidence that more frequent neurological investigations in these patients mean that brain tumors are more likely to be found sooner. There may also be reasons related to the disease that could increase the risk for urinary organ cancers, resulting from chronic irritation to those organs as a result of MS. However, individual risk of developing urinary organ cancer is modest, as less than 0.2 percent of people with MS developed this cancer for every 10 years of follow-up."

Bahmanyar also noted that people with MS have on average a lower body mass index (BMI) than the general population, and BMI is a risk factor for several types of cancer, so the lower body weight may explain some of the reduction in cancer risk. It is also possible that some reduction in cancer risk results from the way the body responds to MS.