Thymic cancer is a rare cancer that presents with symptoms such as a persistent cough, breathing difficulties or chest pain. The thymus is an organ in the chest, behind the breastbone. The thymus is part of your body’s lymphatic system and immune system. The thymus helps the body to make a type of white blood cell. These cells protect you against infections. Thymic cancer is rare. You are more likely to get it if you have other diseases such as myasthenia gravis, lupus, or rheumatoid arthritis. The diagnosis is made on the basis of physical examination, imaging studies and a biopsy. The most common treatment is surgery to remove the tumor. Other options include radiation therapy, chemotherapy, and hormone therapy.

• What is thymus cancer?
• Types of thymus cancer

• Thymoma
• Thymic carcinoma
• Thymic carcinoid

• Cause of thymus cancer
• Risk factors

• Age
• Origin

• Symptoms caused by the tumor
• Examination and diagnosis

• Medical history and physical examination
• Visual art investigation
• Blood tests
• Biopsy (tissue examination)

• Treatment of thymus cancer
• Prognosis and survival
• Prevention

 The thymus is located behind the sternum / Source: Nerthuz/Shutterstock.com

What is thymus cancer?

The thymus is an organ in your chest, below the breastbone. The thymus is part of your body’s lymphatic system and immune system. This organ produces white blood cells called lymphocytes, which help fight infections. There are two main types of thymic cancer: thymoma and thymic carcinoma. Both are very rare. Thymic carcinoma is more aggressive and more difficult to treat than thymoma. People with thymoma usually also have an autoimmune disease, such as myasthenia gravis (MG), erythrocytic aplasia (PRCA), and rheumatoid arthritis (RA).

Types of thymus cancer

Three types of thymus cancer are distinguished.

Thymoma

This form of thymus cancer is the most common and consists of a combination of different types of cells in the thymus:

• epithelial cells: the tissue that covers organs
• lymphocytes: type of white blood cells

Thymoma is a slow-growing cancer that almost never spreads to the lungs or the lining of the lungs.

Thymic carcinoma

Thymic carcinoma arises from epithelial cells and this form of thymus cancer usually grows faster than a thymoma. Metastasis is often already present by the time the doctor makes the diagnosis.

Thymic carcinoid

Thymic carcinoid (neuroendocrine carcinoma) is rare and grows slowly. This cancer arises from neuroendocrine cells.

Cause of thymus cancer

In 2023, not much is known about why thymus cancers develop in some people but not others. Researchers have found some DNA changes that are more common in thymus cancer cells than in normal cells. However, they still don’t know why these changes occur in some people and how the changes occur.

Risk factors

There are no specific hereditary, environmental or lifestyle risk factors associated with thymoma or thymic carcinoma. There is a possible link with radiation exposure of the upper chest, but this has not yet been confirmed as of 2023. The only known risk factors are age and ethnicity.

Age

The risk of this type of cancer increases with age. Thymic cancer is rare in children and young adults, is more commonly seen in middle-aged adults, and is most common in people aged 70 and older.

Origin

In the United States, this cancer is most common in Asians and Pacific Islanders and least common in whites and Latinos. It is more common in African Americans than in whites.

Symptoms caused by the tumor

The thymus is located in the center of the chest, near the airways and certain blood vessels. Tumors in the thymus can press on nearby structures and cause symptoms such as:

• shortness of breath

Drumstick fingers / Source: Desherinka, Wikimedia Commons (GFDL)

• cough (which may produce bloody sputum or mucus)
• chestpain
• problems swallowing
• loss of appetite
• weight loss
• (sometimes) drumstick fingers

The thymus is located near the superior vena cava, the main blood vessel that carries blood from the head and upper body to the heart. Tumors pressing on this vessel can cause symptoms of superior vena cava syndrome. This involves partial or complete occlusion of the superior vena cava, causing the following symptoms:

• swelling in the face, neck and upper chest, sometimes with a bluish color
• swelling of the visible veins in this part of the body
• headache
• dizzy or light-headed

Examination and diagnosis

If you suspect thymus cancer, the doctor will ask you questions about the symptoms and perform one or more examinations or tests. Certain signs and symptoms may indicate a thymic tumor, but tests are needed to know for sure.

Medical history and physical examination

If you have symptoms or signs that indicate you may have a thymus tumor, your doctor will take a complete medical history. You will also be asked about the complaints you experience and your general health. A physical examination provides information about possible signs of thymus cancer and other health problems.

Visual art investigation

Imaging tests use X-rays, magnetic fields, or radioactive substances to create images of the inside of your body. Imaging studies may be done for a number of reasons, including:

• To find a suspicious area that may be cancerous.
• To know how far cancer has spread.
• To see if the treatment is working.
• Looking for signs that cancer has returned.

 MRI scan / Source: Istock.com/© james steidlImaging research may include:

• Chest X-ray : An X-ray of the chest (thorax) showing the heart and lungs.
• CT scan : This uses X-rays to create detailed, cross-sectional images of your body. Unlike a regular X-ray, a CT scan creates detailed images of the soft tissues in the body.
• MRI scan : Like CT scans, MRI scans provide detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of X-rays. An MRI of the breast can be done to get a better look at thymus tumors.
• PET scan : for a PET scan you are injected with a slightly radioactive form of sugar, which mainly collects in cancer cells. A special camera is then used to create an image of areas of radioactivity in the body. The image is not as detailed as a CT or MRI scan, but a PET scan can look for possible areas of cancer that has spread.

 Normal chest x-ray of a young person (slim, good inspiration position) / Source: Chikumaya, Wikimedia Commons (CC BY-SA-3.0)

Blood tests

Blood tests cannot be used to diagnose thymoma, but it can be useful in some situations. For example, blood tests may be done to look for certain antibodies if myasthenia gravis (MG) or another autoimmune disease is suspected. When thymoma is diagnosed, blood tests are done to get an idea of a person’s overall health, especially if surgery is planned.

Biopsy (tissue examination)

Although your symptoms and imaging tests may indicate that thymus cancer is likely present, the diagnosis can only be made with certainty by examining suspicious tissue under a microscope. But it is not always necessary to perform a biopsy.

Treatment of thymus cancer

You may receive one or more of the following treatments:

• operation
• irradiation
• chemotherapy

The most common surgery for thymic tumors is the complete removal of the thymus gland (including the tumor). This is called a thymectomy. In most cases the operation is performed via a median sternotomy. This is an incision (cut) in the center of the chest that splits the breastbone, after which the entire thymus and tumor can be removed. The surgeon will also attempt to remove any areas of tumor outside the thymus. So if the tumor has grown into nearby structures, the surgeon may need to remove parts of those structures as well. This may involve removing parts of the pleura (tissue covering the lungs), pericardium (the pericardium), nerves, the superior vena cava (a large vein leading to the heart) and/or the lungs.

Prognosis and survival

The five-year survival rate is the percentage of patients who are still alive five years after the diagnosis of thymus cancer. Of course, many people live much longer than 5 years (and many are declared cancer-free). Although many patients live much longer than five years, it is not always an indication that the cancer has been cured, as some thymus tumors grow very slowly and in some other people may return several years after treatment.Because thymus cancer is uncommon, it is difficult to find accurate survival rates based on the stage of the cancer. The figures below come from a large series of patients treated in Japan between 1990 and 1994. They look separately at patients with thymoma (type A, AB and B) and thymic carcinoma (type C thymoma). These are also observed survival rates. These are older numbers and progress has been made since then in treating cancer.

Prevention

Because in 2023 it is not known exactly what causes thymus cancer, it is not yet possible to provide advice on how to prevent this form of cancer.

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