ConditionCancer
Thymoma
A thymoma is a rare tumor that starts in the thymus, a small gland behind the breastbone that helps train immune cells. Most thymomas grow slowly and are found by chance on a chest scan, or because of symptoms such as cough, chest pain or breathlessness. About a third of people have an associated autoimmune condition, most often myasthenia gravis, which causes muscle weakness, drooping eyelids and double vision. Surgery to remove the thymus is the main treatment, and the outlook is very good for early-stage tumors.
Also called: Thymic epithelial tumor, thymus tumor, thymic carcinoma (aggressive related type)
At a glance
- What it is
- A tumor of the epithelial cells of the thymus, in the front of the chest.
- Who gets it
- Usually adults aged 40 to 70.
- Symptoms
- Often none; cough, chest pain, breathlessness; symptoms of myasthenia gravis.
- Associated conditions
- Myasthenia gravis, pure red cell aplasia, low antibody levels (Good syndrome), other autoimmune diseases.
- Treatment
- Surgical removal (thymectomy); radiation and chemotherapy for advanced disease.
When to get help
Call 911 or go to the ER
- Severe breathlessness, difficulty swallowing or speaking, or weakness of breathing muscles (possible myasthenic crisis)
- Swelling of the face, neck and arms with prominent chest veins and breathlessness (possible superior vena cava syndrome)
See a doctor within a day or two
- Drooping eyelids, double vision or weakness that gets worse through the day
- Persistent chest pain, cough or breathlessness with a known chest mass
Book a routine appointment
- A mass in the front of the chest found on an X-ray or CT scan
- Persistent tiredness and pale skin (possible anemia from red cell aplasia), or frequent infections
What the thymus does
The thymus sits in the anterior mediastinum, the space in front of the heart and behind the breastbone. It is large in childhood and helps T lymphocytes mature, then shrinks and is replaced by fat in adults. Thymomas arise from its epithelial cells and can disrupt immune tolerance, which explains the link with autoimmune disease.
Symptoms
Many thymomas cause no symptoms. When they do:
- local symptoms: cough, chest pain or pressure, breathlessness, hoarseness, difficulty swallowing
- superior vena cava syndrome: swelling of the face, neck and arms if the tumor presses on the large vein
- myasthenia gravis symptoms: drooping eyelids, double vision, difficulty chewing or swallowing, limb weakness that worsens with activity
- general symptoms: fatigue, weight loss, fever, night sweats (less common)
Associated conditions (paraneoplastic syndromes)
| Condition | How often | Effects |
|---|---|---|
| Myasthenia gravis | 30% to 50% of people with thymoma | Fatigable muscle weakness |
| Pure red cell aplasia | About 5% | Severe anemia |
| Good syndrome (hypogammaglobulinemia) | Uncommon | Low antibodies, recurrent infections |
| Other autoimmune diseases | Variable | Lupus, thyroiditis, neuromyotonia, others |
About 10% to 15% of people with myasthenia gravis have a thymoma, so everyone diagnosed with myasthenia should have a chest CT scan.
Diagnosis
- CT scan of the chest with contrast: the main test, showing size, location and invasion
- MRI or PET scan in some cases
- blood tests: acetylcholine receptor antibodies, blood count and antibody levels
- biopsy: often not needed before surgery if the tumor appears resectable, but used for larger or invasive tumors, or when lymphoma or a germ cell tumor is possible
Staging and type
Thymomas are classified by the WHO into types A, AB, B1, B2 and B3, from least to most aggressive. Thymic carcinoma (type C) is a more aggressive related cancer. Staging (Masaoka-Koga or TNM) describes whether the tumor is contained within its capsule or has invaded nearby structures or spread.
Treatment
- Surgery: complete removal of the thymus and tumor (thymectomy), through the breastbone or by minimally invasive (robotic or VATS) approaches. Complete removal is the most important factor for cure.
- Radiation therapy: after surgery for invasive tumors or incomplete removal.
- Chemotherapy: to shrink large tumors before surgery, or for advanced or recurrent disease.
- Treating myasthenia gravis: before surgery, symptoms must be well controlled to avoid breathing problems during recovery. Thymectomy often improves myasthenia over time.
- Follow-up: CT scans for many years, because thymomas can recur late.
Outlook
Early-stage thymomas that are completely removed have excellent outcomes, with 10-year survival above 90%. Invasive and advanced thymomas, and thymic carcinomas, have a less favorable outlook but can still often be controlled for years.
Frequently asked questions
What are the symptoms of thymoma?
Many people have no symptoms. Others have cough, chest pain, breathlessness or difficulty swallowing. Up to half develop myasthenia gravis, causing drooping eyelids, double vision and muscle weakness that worsens with activity.
Is thymoma cancer?
Thymoma is considered a cancer because it can invade nearby tissues and occasionally spread, but most grow slowly and are cured with surgery. Thymic carcinoma is a related but more aggressive cancer of the thymus.
What is the link between thymoma and myasthenia gravis?
Thymomas can disrupt how the immune system learns to tolerate the body's own tissues, leading to antibodies that attack nerve-muscle connections. That is why up to half of people with thymoma develop myasthenia gravis, and why people with myasthenia are screened for thymoma.
What is the survival rate for thymoma?
Survival is high for early-stage thymomas, with 10-year survival above 90% after complete removal. Outcomes are lower for advanced or invasive tumors and thymic carcinoma, but treatment can still provide long-term control.
Sources
This guide was written from current patient and clinical guidance, including:
- National Comprehensive Cancer Network (NCCN): Guidelines for Thymomas and Thymic Carcinomas
- National Cancer Institute: Thymoma and thymic carcinoma treatment (PDQ)
- American Cancer Society: Thymus cancer
- Myasthenia Gravis Foundation of America: Thymectomy
- International Thymic Malignancy Interest Group: Staging and resources