Most Common Adult Muscular Dystrophy Linked to Increased Cancer RiskAdults with myotonic muscular dystrophy (MMD), an inherited disorder marked by progressive muscle wasting and weakness, may be at increased risk of developing cancer, a new study suggests. A research team led by Dr. Mark H. Greene and Dr. Shahinaz M. Gadalla, both of the Clinical Genetics Branch in NCI’s Division of Cancer Epidemiology and Genetics, found that patients with MMD from two independent cohorts had a twofold higher overall risk of cancer compared with people in the general population, with the increased risk mainly accounted for by cancers of the colon, brain, endometrium, and ovary. The results were reported in the December 14 issue of JAMA.
MMD is the most common form of muscular dystrophy that begins in adulthood. There are two types of MMD, type 1 and type 2, which affect multiple body systems and are caused by mutations in different genes. The signs and symptoms of the two types overlap, although type 1 is more severe.
“The impetus for this work came from [coauthor] Dr. Richard Moxley’s clinical impression that the cancer occurrence among his MMD patients was greater than expected,” Dr. Greene noted. The question then was whether those cancers were part of the MMD syndrome or just a coincidental finding.
To address this question, the researchers linked the health records of 1,658 MMD patients from two nationwide patient registries, one in Sweden and one in Denmark, to the corresponding national cancer registry in each country. They found the same patterns of increased cancer risk in both the Swedish and Danish MMD cohorts, which “provides substantial reassurance that our observations are genuine,” the study authors wrote.
“This study is the first formal quantitative assessment of cancer risk in MMD, which previously has not been considered a cancer susceptibility disorder,” Dr. Greene said.
“We don’t yet know for sure why MMD patients are at increased risk of cancer,” added Dr. Gadalla. “It may be that some of the genetic changes that cause MMD symptoms are also responsible for the increase in cancer risk.” Further research to explore the possible mechanisms involved may provide new insights into mechanisms of carcinogenesis, she noted.
In addition to pursuing that avenue of research, Dr. Greene and his colleagues are investigating whether the cancer risk differs between patients with type 1 versus type 2 MMD, and whether the excess risk can be explained by known risk factors for cancer—questions that this study could not answer.
In the meantime, Dr. Greene said, “It’s important that clinicians be aware of this possible increased risk of cancer in MMD patients.”
NCI Cancer Bulletin for December 13, 2011 - National Cancer Institute