ORLANDO – Patients with multiple sclerosis are at significantly reduced risk of being diagnosed with cancer, compared with the general population, but delayed cancer detection – that is, diagnostic neglect – appears to be a contributing factor, a study from British Columbia has shown.
"Diagnostic neglect is unlikely to account for the entire reduced cancer risk that we’re seeing, but I think it could have major implications for the health, well-being, and longevity of people with multiple sclerosis," said Helen Tremlett, Ph.D, a neuroepidemiologist at the University of British Columbia, Vancouver.
In the population-based Malignancy and Multiple Sclerosis (MaMS) study, she and her coinvestigators linked data from the British Columbia MS registry with the provincial cancer registry. The study included 6,820 MS patients who visited a British Columbia MS clinic in 1980-2004. Most had never been exposed to an immunomodulatory therapy. They had a collective 110,666 person-years of follow-up. Their cancer incidence over time was compared with that of the age-, sex-, and calendar year–matched general population of British Columbia.
Bruce Jancin/IMNG Medical Media
Dr. Helen Tremlett
The standardized incidence ratio for all cancers in the MS cohort was 0.86, meaning MS patients had a highly significant overall 14% reduction in the risk of being diagnosed with cancer. The risk reduction was particularly striking for colorectal cancer: Patients with MS were 44% less likely than controls to be diagnosed with this malignancy.
The cancer risk reductions were similar in men and women with MS, and in those with relapsing-remitting as compared with primary progressive MS, Dr. Tremlett reported at the fifth Cooperative Meeting of the Consortium of Multiple Sclerosis Centers and the Americas Committee for Treatment and Research in Multiple Sclerosis.
Of note, the cancer risk reduction identified in the MaMS study was consistent with an earlier meta-analysis of five studies by other investigators around the world, who concluded that the risk of being diagnosed with cancer was 8% lower in MS patients than controls, a statistically significant difference (J. Neurol. Neurosurg. Psychiatry 2010;81:1413-4).
Unlike the other researchers, however, Dr. Tremlett and her coworkers also looked at tumor size at the time of diagnosis for the four most common cancers: breast, prostate, lung, and colorectal cancer. They found a consistent pattern: MS patients diagnosed with cancer had a lower-than-expected rate of the smaller T1 and T2 tumors than in the matched general population with cancer, and a greater-than-expected rate of T3 and T4 tumors.
The most likely explanation for the observed larger-than-expected tumor size is that when MS patients report, say, a new sense of fatigue, it may be ascribed to their MS, whereas if a patient from the general population had the same complaint, a battery of tests would be ordered, she said.
The MS patients’ 14% reduction in the risk of being diagnosed with cancer had an impressive P value. In contrast, the association between MS and larger tumor size, while statistically significant, had a less than stellar P value of .04. For this reason, Dr. Tremlett said she doesn’t believe diagnostic neglect is the entire explanation for the MS patients’ reduction in cancer incidence. Other possible contributing factors worthy of further study are that MS patients’ hypervigilant immune system renders them less vulnerable to cancer growth, or that MS and cancer share a common and as-yet-unidentified genetic predisposition, or that upon receiving the diagnosis of MS, affected patients adopt a healthier lifestyle.
Dr. Tremlett stressed the importance of being on the lookout for cancer and other aging-related comorbidities, especially now that patients with MS are living longer. In a recent study of 6,917 MS patients in British Columbia, she and her coinvestigators determined that the median survival age was 78.6 years for women and 74.3 years for men. Those are some of the longest life spans ever reported, but still about 6 years less than expected for the general British Columbia population.
Median survival from disease onset was markedly longer for patients with relapsing-onset MS than primary progressive MS: 49.7 years compared with 32.5 years. However, the two groups lived to about the same age.
Patients with primary progressive MS had a 1.52-fold greater relative mortality risk than did those with relapsing-onset MS. Women with primary progressive MS had a 1.55-fold survival disadvantage compared with men with primary progressive disease (J. Neurol. Neurosurg. Psychiatry 2012;83:61-6).
The MaMS study is sponsored by the Canadian Institutes of Health Research and the Multiple Sclerosis Society of Canada. Dr. Tremlett reported having no relevant financial disclosures.