Thymoma is a tumor that originates in the thymus. The thymus is an organ that is part of the immune system.

Thymomas are usually benign tumors, but they can also be malignant. Thymomas are rare tumors often associated with an autoimmune disease, the most common of which is myasthenia gravis.

Myasthenia gravis is a neuromuscular disease seen in approximately 15% of cases. There are three types of thymoma called Type A, Type B and Type C. They are classified based on the shape of the cells under a microscope. Type C is a combination of the cells found in Type A and Type B.

Signs and Symptoms

About one third to one half of thymoma have no symptoms. They are found accidentally during scans for other issues. Some tumors begin to cause problems for people when they grow so large that they press against surrounding tissue and organs.

Diagnosis

As mentioned above, as many as half of thymoma have no symptoms and are found accidentally. Another third of them are found due to the patient’s autoimmune disease.

Doctors will perform a physical exam, blood tests and CT scans to find out as much as possible about the tumor. Often with thymoma though the final diagnosis is not completed until after the tumor is surgically removed and a biopsy is done. The Masaoka staging system is widely used when staging thymoma.

Treatment

The main treatment for thymoma is surgery. If a tumor is already very large chemotherapy and radiation are sometimes used prior to surgery to try to shrink the size of the tumor. If the tumor has invaded surrounding tissue chemotherapy and radiation are sometimes also used after surgery.

Prognosis

The prognosis for thymoma in the early stages is quite good. Unfortunately the prognosis is not as positive for later stages of thymoma. Thymomas metastasize in approximately 7% of cases. Patients have lived for several years even with late stage thymoma.