Prognosis of Thymic Carcinoma Patients Not Affected by MG: Study

Myasthenia occurs in 10% of patients with malignant tumor in their thymus gland

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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About one in 10 patients with thymic carcinoma — a rare type of malignant tumor in the thymus gland — also has myasthenia gravis (MG), but this does not appear to reduce their lifespan, according to a study of data from an international registry.

The study, “Does myasthenia gravis affect long-term survival in thymic carcinomas? An ESTS database analysis,” was published in the journal Diagnostics.

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MG happens when the immune system mistakenly makes antibodies that interfere with the normal communication between nerve and muscle cells. Muscles begin to weaken and waste, resulting in symptoms such as muscle weakness and fatigue.

Sometimes, the disease occurs secondary to a thymoma, a tumor that forms in the cells that cover the outside lining of the thymus. The thymus is a gland-like organ that helps the body’s immune response by nesting T-cells, a type of immune cell that help defend the body against invaders.

In many patients diagnosed with MG, the thymus is larger than normal and rich in clusters of another type of immune cells called B-cells, which may contribute to how MG develops. However, it is not clear how MG affects the likely course of a thymoma.

What is thymic carcinoma?

Thymic carcinoma is a rarer and more aggressive type of tumor in the thymus. The percentage of patients who remain alive five years after a diagnosis is about half that of patients with a thymoma. It is also linked to MG, but MG appears to occur less frequently in patients with a thymic carcinoma than in those with a thymoma (less than 15% vs. 30%–40%).

To understand the prevalence of MG in patients with thymic carcinoma, and how it affects their survival, a team of international researchers drew on data from 203 patients registered in a database from the European Society of Thoracic Surgeons (ESTS).

The study included 107 female and 96 male patients. Their mean age was 59.7 years. In the period from January 2000 until July 2019, all had undergone surgery to remove the tumor, alone or in combination with chemotherapy and/or radiotherapy. Their mean follow-up was 60 months (around five years).

Before surgery, 22 patients (10.8%) underwent induction therapy to shrink the tumor before it was removed. The surgery was often done by cutting through the sternum (38.4%), but an incision into the chest wall (16.3%) and less-invasive approaches like robotic (8.4%) and video-assisted surgery (4.9%) were also used.

Complete resection, that is, complete tumor removal, was achieved in 158 patients (77.8%). The percentage of patients who remained alive five years after their diagnosis (their five-year survival) was 75%; at 10 years, it was 63%.

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Of the 203 patients, 22 (10.8%) also had MG. There were no data about the onset of MG in relation to that of the tumor, but MG did not occur as a complication of the surgery. The disease was more common among patients 60 years and older (63.6% vs. 36.4% in younger patients) and in male patients (77.3% vs. 22.7%).

The presence of MG did not significantly reduce patients’ five-year survival, which was 78% in patients without MG versus 50% in those with MG.

“Myasthenia occurred in about 10% of thymic carcinomas and it did not seem to affect significantly the long-term prognosis in surgically treated thymic carcinoma patients,” the researchers wrote.

However, some other factors may be linked to better prognosis and “could be considered in the daily clinical practice,” the researchers wrote. For example, being younger than 60 years, achieving complete resection, and undergoing postoperative radiotherapy were all linked to better five-year survival.