Thymoma

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.

Signs and Symptoms

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.

Diagnosis and Tests

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.