MG may be linked with higher extrathymic cancer incidence: Study
Retrospective analysis finds incidence higher within 5 years of diagnosis
People with myasthenia gravis (MG) have a higher risk of developing cancer in organs other than the thymus, particularly in the skin and gastrointestinal tract, than people without the disease, according to a study.
The incidence of such cancers tended to be higher in the five years before and after an MG diagnosis, indicating the disease may “behave as a paraneoplastic disorder,” a disease that occurs in association with cancer, the researchers wrote.
The study, “The Association Between Myasthenia Gravis and Higher Extrathymic Cancer Risk,” was published in Brain and Behavior.
MG is an autoimmune condition caused by self-reactive antibodies that attack proteins necessary for the proper function of the neuromuscular junction, the site where nerve and muscles cells communicate to coordinate voluntary movements. It has been associated with tumors in the thymus gland, an organ of the immune system that produces immune cells, in 15% to 20% of patients. However, it’s “debatable” whether MG is “also associated with extrathymic [outside-the-thymus] cancers” or whether it “can be considered a paraneoplastic disorder for extrathymic cancers,” the researchers wrote.
Checking for cancer incidence
The researchers conducted a retrospective analysis of MG patients at a specialized care facility in Israel from January 2000 to May 2023.
They looked at 436 patients, 54% of them women, with a median age of 55.7 at the time of disease onset, and followed them for a median of three years.
Most (75.6%) had antibodies targeting acetylcholine receptors, while 2.7% had antibodies targeting muscle-specific kinase (MuSK), and 21.6% had neither anti-AChR nor anti-MuSK antibodies.
Of the 418 MG patients with available data, 41% had a documented cancer. Of these, 32% had extrathymic cancer, 12% had thymus tumors, and 3% with both thymic and extrathymic cancer. Extrathymic cancers in these patients most commonly affected the skin (29.9%) and gastrointestinal tract (23.9%). In 61% of the cases, extrathymic cancers were diagnosed after the onset of MG, while in 39% they were diagnosed before MG onset.
MG patients had significantly higher rates of extrathymic cancer than 3,925 age- and sex-matched controls. The control subjects were patients without MG who had been referred to the facility’s neurology, rheumatology, or internal medicine departments.
Analyses also indicated that MG patients had a risk of developing cancer that was almost three times higher than that of patients who had been referred to the rheumatology department due to other conditions.
The incidence of extrathymic cancer was significantly higher within the paraneoplastic time window — the five years before and after an MG diagnosis — in MG patients (21.3%) compared with controls from internal medicine (16.6%), neurology (6.2%), and rheumatology (6.2%).
“Whether this increase in extrathymic cancer is simply due to coincidence, thymic removal, environmental, or genetic factors predisposing for both the MG and cancer are unclear and require further research,” the researchers wrote.
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