Late-Onset Myasthenia Gravis Linked to Higher Cancer Risk

Daniel M. Keller, PhD

July 02, 2013

BARCELONA, Spain — Myasthenia gravis (MG), especially if it is of late onset, carries a high risk for cancers outside of the thymus. These extrathymic malignancies were heterogeneous in their organs of origin, and all were solid tumors, a new study shows.

"We found no relation to any particular type of tumor," Anna Pellisé, MD, from the Neurology Department at the Joan XXIII University Hospital in Tarragona, Spain, reported here at the 23rd Meeting of the European Neurological Society (ENS).

MG is considered a paraneoplastic disease when accompanying thymoma, affecting up to 40% of patients who have thymoma, Dr. Pellisé showed. Further, patients with thymoma are at higher risk for a secondary malignancy whether they have MG or not. But MG itself is a risk factor for extrathymic malignancies regardless of the presence or absence of thymoma.

Older MG Patients at Risk for Extrathymic Neoplasms

Previous studies have produced conflicting results about the prevalence of extrathymic malignancies in patients with MG. Through a single-center retrospective chart review of 38 patients diagnosed with MG between 2002 and 2012, Dr. Pellisé and colleagues assessed the prevalence of extrathymic neoplasms and compared the clinical characteristics and treatments of MG patients with or without these malignancies.

The mean age of the entire group of patients with MG was 56.2 ± 22.1 years. The group comprised 16 women and 22 men. All but 1 were positive for antibodies to the acetylcholine receptor. One had an autoimmune disease, and 9 (23.6%) had thyroid disease.

Age was the only variable that statistically significantly differed between the patients with or without neoplasms (P = .013).

No patients younger than 50 years of age (n = 13) had a neoplasm. However, 12 of the 25 patients over 50 had an extrathymic neoplasm but no other autoimmune or thyroid disease. Patients with neoplasm clustered mostly in the 61- to 80-year range. Diagnosis of a neoplasm occurred mainly around the time of the MG diagnosis. Six of the 12 neoplasms were diagnosed from 1 year before to 1 year after the MG diagnosis. However, 2 were diagnosed more than 5 years before MG, 1 was diagnosed 3 years after the onset of MG, and 3 were diagnosed more than 5 years after MG.

The 12 tumors were of 9 different types: 2 each of squamous cell carcinoma of the mouth, invasive bladder cancer, or prostate adenocarcinoma, and 1 each of basal cell skin cancer; lung, gastric, breast, or colon adenocarcinoma; and renal cell cancer.

At the onset of MG, most (n = 9) of the patients with tumors had generalized symptoms of MG, although 1 had ocular symptoms and 2 had bulbar symptoms (affecting muscles innervated by various cranial nerves).

This study confirms some previous ones showing that age is a factor in the elevated prevalence of cancer in patients with MG. Dr. Pellisé recommended further studies focusing on patients with late-onset MG. In addition, she advised appropriate surveillance of older patients with MG for extrathymic malignancies if her results are confirmed.

Asked to comment, session moderator Riccardo Soffietti, MD, professor of neurology and neuro-oncology at the University Hospital of Turin, Italy, who was not involved in the research, told Medscape Medical News, "It is not surprising that some patients with the disease who received immunosuppressant treatment, steroid treatment for a long time, can have some risk of secondary tumors."

But he also noted that "probably as in many human diseases there is an issue of genetic propensity. Different subgroups of patients [have] different propensity, for instance, to have different toxic reactions to drugs and so on, adverse events, secondary tumors. The genetic susceptibility can be very variable obviously."

The study received no commercial funding. Dr. Pellisé and Dr. Soffietti have disclosed no relevant financial relationships.

23rd Meeting of the European Neurological Society (ENS). Abstract O258. Presented June 9, 2013.

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