Thymoma
A tumor arising from the thymus gland in the chest
Quick Facts
- Type: Tumor of the thymus gland
- Location: Upper chest, behind the breastbone (mediastinum)
- Key link: Often associated with myasthenia gravis
- Main treatment: Surgery to remove the tumor
Overview
A thymoma is a tumor that develops from the cells of the thymus, a small gland located in the upper chest behind the breastbone. The thymus is part of the immune system and is most active in childhood, helping immune cells called T cells to mature. Thymomas are uncommon and usually grow slowly.
Thymomas are often discovered because they are linked to autoimmune conditions, especially myasthenia gravis, a disease that causes muscle weakness. Some thymomas are found by chance on a chest scan done for another reason. While many thymomas are slow-growing, a related, more aggressive tumor called thymic carcinoma also exists.
How a thymoma behaves depends on its type and whether it has grown into nearby tissue or spread. For this reason, doctors classify thymomas based on what the tumor looks like under the microscope and how far it has extended. This information guides treatment decisions and helps predict the outlook, which is generally favorable for tumors found early and removed completely.
Symptoms
Many thymomas cause no symptoms at first. When symptoms occur, they may come from the tumor itself or from an associated autoimmune condition:
- Cough, chest discomfort, or a feeling of pressure in the chest
- Shortness of breath
- Muscle weakness, drooping eyelids, or double vision (often from myasthenia gravis)
- Trouble swallowing or a hoarse voice if the tumor presses on nearby structures
Swelling of the face, neck, or upper body can occur if a larger tumor presses on a major vein, and this should be evaluated promptly.
Causes
The exact cause of thymoma is not known. It develops when cells of the thymus grow abnormally and form a tumor. Unlike some cancers, thymoma is not strongly linked to lifestyle factors such as smoking.
Thymomas are closely tied to disorders of the immune system. Many people with a thymoma also have an autoimmune condition, in which the immune system attacks the body's own tissues. Myasthenia gravis is the most common of these, but others can occur as well.
Risk Factors
- Having myasthenia gravis or another autoimmune condition
- Middle age, as thymomas most often occur in adults between roughly 40 and 70 years of age
There are no well-established lifestyle risk factors for thymoma. It affects men and women fairly equally and is not caused by anything a person did.
Diagnosis
Diagnosis usually combines imaging with examination of tissue:
- Imaging: A CT scan of the chest, sometimes with MRI, shows the size and location of the tumor and whether it has spread to nearby tissue.
- Biopsy or surgery: A sample of the tumor, or the whole tumor removed at surgery, is examined under a microscope to confirm the diagnosis and classify it.
- Blood and nerve tests: If myasthenia gravis is suspected, blood tests and nerve-muscle testing help confirm it before surgery.
Treatment
Treatment depends on the tumor's size, whether it has spread, and the person's overall health.
- Surgery: Removing the thymus and tumor is the main treatment and can cure many thymomas, especially when caught early.
- Radiation therapy: This may be used after surgery if the tumor has grown into nearby tissue or could not be fully removed.
- Chemotherapy: For tumors that have spread or cannot be removed, chemotherapy may be used, sometimes before surgery to shrink the tumor.
- Treating myasthenia gravis: If present, this autoimmune condition is managed alongside the tumor, and removing the thymus can sometimes improve it.
Because thymomas can return years later, long-term follow-up with imaging is usually recommended. Even after a tumor is fully removed, periodic chest scans help catch any recurrence early, when it is most treatable, so people are encouraged to keep their follow-up appointments.
When to See a Doctor
See a doctor for ongoing chest discomfort, an unexplained cough, or new muscle weakness, drooping eyelids, or double vision. Seek emergency care right away if you have:
- Sudden or severe difficulty breathing or swallowing
- Swelling of the face, neck, or arms with a feeling of fullness in the head
- Severe weakness affecting breathing, which can be a complication of myasthenia gravis
These can signal that a tumor is pressing on important structures or that an autoimmune crisis is developing.
Frequently Asked Questions
Is a thymoma cancer?
A thymoma is a tumor of the thymus gland that can behave in a benign or more invasive way. Many grow slowly and can be cured with surgery. A related, more aggressive tumor called thymic carcinoma is more clearly cancerous.
Why is thymoma linked to myasthenia gravis?
The thymus helps regulate the immune system, and thymomas can disturb this balance. Many people with a thymoma also have myasthenia gravis, an autoimmune disease that causes muscle weakness. Removing the thymus can sometimes improve it.
How is a thymoma treated?
Surgery to remove the thymus and tumor is the main treatment and can cure many thymomas caught early. Radiation or chemotherapy may be added if the tumor has grown into nearby tissue or spread.
What symptoms does a thymoma cause?
Many cause no symptoms and are found on a scan. Others cause cough, chest pressure, or shortness of breath, or signs of myasthenia gravis such as muscle weakness, drooping eyelids, and double vision.
Can a thymoma come back after treatment?
Yes. Thymomas can return years after surgery, so long-term follow-up with imaging is usually recommended even after the tumor is removed.
References
- National Cancer Institute (NCI). Thymoma and Thymic Carcinoma Treatment.
- MedlinePlus, U.S. National Library of Medicine. Thymoma.
- Mayo Clinic. Thymoma and thymic carcinoma.
- National Organization for Rare Disorders (NORD). Thymoma.