Thymomas are rare tumors of the thymus gland. Rarely, other tumors such as lymphomas, leukemias and germ cell tumors can be found in the thymus gland. The commonest age to be diagnosed with a thymoma is between 40 and 60 years.
Most thymomas are slow-growing tumors. Their behavior is classified as either non-invasive or invasive. Non-invasive tumors are completely enclosed within the thymus gland; invasive tumors have broken through the edge of the thymus gland and have begun to spread into surrounding tissues in the chest. Usually this is confined to the chest area and it is very rare for thymomas to spread to other parts of the body. Slightly under half of all thymomas are invasive.
Symptoms include chest pain, a persistent cough, shortness of breath, difficulty in swallowing and hoarseness of the voice.
The fact that the thymus gland is involved in the development of the early immune system means that some people with thymomas have other illnesses related to this. The most common of these is a condition called myasthenia gravis. The main feature of this condition is increased fatigue of certain muscle groups, which means that when those muscles are used they become weak very quickly. Somewhere between 30% and 50% of people with a thymoma will also have myasthenia gravis.
It is often difficult to be clear whether a thymoma is malignant or not. Doctors can usually tell by taking a tissue sample (biopsy) and looking at it under a microscope. The microscopic appearance of benign (non-malignant) and cancerous tumors are often similar in this case. This usually means that doctors have to rely on the behavior of the thymoma (whether it is invasive or non-invasive) to decide if it is cancerous, rather than using a biopsy as the only diagnostic. In other words, a thymoma that is non-invasive may be considered benign, whereas one that had invaded the surrounding tissue (or elsewhere) would be considered cancerous.
About 15% of patients with myasthenia gravis are found to have a tumor of the thymus gland, known as a thymoma. Most thymomas are benign. Also, about 50% of patients with thymoma are found to have myasthenia gravis.
If surgery is not possible then radiotherapy can be given. This will not usually cure the condition but, because these tumors are usually slow-growing, will often control it for many years.
Chemotherapy is sometimes given along with radiotherapy and can also be used when the tumor has spread to other parts of the body. These tumors often respond to chemotherapy. Drugs that have been shown to be useful include doxorubicin (Adriamycin), cisplatin, Ifosfamide, etoposide and paclitaxel (Taxol). Because these tumors are rare it is not known which is the best combination of drugs, but chemotherapy can often control the tumor for long periods.
Surgery is the main treatment for thymoma. When the tumor is non-invasive, completely removing it will cure the condition in most people. If the tumor is invasive, surgery may be more difficult and radiotherapy is usually given after surgery, to treat any remaining tumor and reduce the risk of the tumor coming back.
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