Thymus Gland Cancer

Thymus gland cancers are rare malignancies that develop in the thymus gland, which sits in the mediastinum (space between the lungs that holds many important structures, including the heart, trachea and oesophagus). The thymus gland is a part of the lymphatic system, which is a network of tissues and organs that help our bodies fight infection and disease.

The thymus gland is responsible for the production and maturation of T lymphocytes, a type of white blood cell that regulates the body’s immune response and helps protect the body from pathogens (any organism that can cause disease). Once developed, the T lymphocytes travel to the lymph nodes in the body, which filter out damaged and potentially harmful cells.

This type of cancer is slightly more common in men, and is most often found in people in their 70’s. However, anyone can develop this disease.

Types of Thymus Gland Cancer

There are two primary types of thymus gland cancer, which are both classified as carcinomas (cancers arising from epithelial cells that line organs). They are differentiated by how the cancer cells look under the microscope, and by their growth patterns.

Thymomas

Thymomas are the most common thymus gland cancer, and originate from epithelial cells in the thymus gland. Thymoma cells look very similar to healthy thymoma cells, tend to be slow-growing, and rarely metastasise. Thymomas are often categorised using a letter system.

Type A

Type A thymomas are the rarest subtype of the disease. They are classified by spindle-shaped or oval shaped cells, which look very similar to healthy thymus gland epithelial cells. Type A thymomas are slow growing, have a low recurrence rate, and often have the best prognosis.

Type AB

Type AB thymomas, or mixed thymomas, have areas with type A and type B thymomas. These tumours are one of the most common subtypes of the disease, often have a good prognosis.

Type B

Type B thymomas are the most common type of thymoma. These tumours often develop quicker than other subtypes, and can be aggressive in some cases. Type B thymomas are often assigned a number to describe cellular appearance:

B1: thymoma is lymphocyte-rich with epithelial cells looking similar to healthy cells. B1 thymomas often have the best prognosis.
B2: thymoma is still lymphocyte-rich, but epithelial cells appear larger and have abnormal nuclei. B2 thymomas are the most common subtype, and can have a good prognosis when caught early.
B3: thymoma has less lymphocytes, and has epithelial cells that look very abnormal. B3 thymomas may not have as good of a prognosis as other type B thymomas.

Thymic Carcinomas

Thymic carcinomas are a rare form of thymus gland cancer that also originates from epithelial cells in the thymus gland. This type of cancer is more aggressive than thymomas, and tend to grow and metastasise at a faster rate. Because of how rare they are, thymic carcinomas are often diagnosed at an advanced stage of disease, and may not have as good of a prognosis as other thymus gland cancers.

Rare Forms of Thymus Gland Cancer

These types of cancers are considered very rare:

Thymic lymphomas - thymus gland cancer that develops only from white blood cells instead of epithelial cells.
Thymic neuroendocrine tumours (thymic NETs) – thymus gland cancer arising from cells that produce and secrete hormones, such as thymulin and thymosin.

Treatment

If a thymus gland cancer is detected, it will be staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body) and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you.

Cancers can be staged using the TNM staging system:

T (tumour) indicates the size and depth of the tumour.
N (nodes) indicates whether the cancer has spread to nearby lymph nodes.
M (metastasis) indicates whether the cancer has spread to other parts of the body.

This system can also be used in combination with a numerical value, from stage 0-IV:

Stage 0: this stage describes cancer cells in the place of origin (or ‘in situ’) that have not spread to nearby tissue.
Stage I: cancer cells have begun to spread to nearby tissue. It is not deeply embedded into nearby tissue and had not spread to lymph nodes. This stage is also known as early-stage cancer.
Stage II: cancer cells have grown deeper into nearby tissue. Lymph nodes may or may not be affected. This is also known as localised cancer.
Stage III: the cancer has become larger and has grown deeper into nearby tissue. Lymph nodes are generally affected at this stage. This is also known as localised cancer.
Stage IV: the cancer has spread to other tissues and organs in the body. This is also known as advanced or metastatic cancer.

Cancers can also be graded based on the rate of growth and how likely they are to spread:

Grade I: cancer cells present as slightly abnormal and are usually slow growing. This is also known as a low-grade tumour.
Grade II: cancer cells present as abnormal and grow faster than grade-I tumours. This is also known as an intermediate-grade tumour.
Grade III: cancer cells present as very abnormal and grow quickly. This is also known as a high-grade tumour.

Once your tumour has been staged and graded, your doctor may recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.

Treatment is dependent on several factors, including location, stage of disease and overall health.

Treatment options for thymus gland cancer may include:

Surgery, potentially including:
- Thymectomy (total or partial removal of the thymus gland).
- Lymphadenectomy (removal of affected lymph nodes).
- Segmentectomy or wedge resection (removal of a portion of a lobe of the lung – only for advanced cancers that have metastasised to the lung).
- Lobectomy (removal of a lobe of a lung – only for advanced cancers that have metastasised to the lung).
- Pericardiectomy (removal of the pericardial layer of tissue covering the heart – only in advanced cancers that have metastasised to the heart).
Radiation therapy.
Chemotherapy.
Hormone therapy.
Targeted therapy.
Immunotherapy.
Clinical trials.
Palliative care.

For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.

Risk factors

Because of how rare thymus gland cancers are, there has been limited research into the risk factors of this disease.

Early symptoms

Symptoms of a thymus gland tumour may include:

Shortness of breath.
Persistent cough.
Chest pain.
Hoarseness of the voice.
Difficulty swallowing.
Superior vena cava syndrome (caused by tumour pressing on the superior vena cava vessel), which carries its own set of symptoms:
- Swelling of the face, neck, and/or upper chest.
- A bluish complexion from the upper chest up.
- Swelling of visible veins from the upper chest up.
- Headaches.
- Dizziness.
Unexplained weight loss and/or loss of appetite.

Not everyone with the symptoms above will have cancer but see your general practitioner (GP) if you are concerned.

Diagnosis/diagnosing

If your doctor suspects you have a thymus gland cancer, they will order a range of diagnostic tests to confirm the diagnosis, and refer you to a specialist for treatment.

Physical examination

Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.

Imaging & blood tests

The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), x-rays, bone scan and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and looks for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions.

Biopsy 

Once the location(s) of the cancer has been identified, the doctor will perform a biopsy to remove a section of tissue using a needle. This can be done by either a fine needle aspiration (FNA), core needle biopsy (CNB), and/or a lymph node biopsy. The samples are then analysed for cancer cells.

Prognosis (Certain factors affect the prognosis and treatment options)

While it is not possible to predict the exact course of the disease, your doctor may be able to give you a general idea based on stage, rate/depth of tumour growth, susceptibility to treatment, age, overall fitness and medical history. Generally, early-stage thymus gland tumours have a good prognosis and survival rates. However, if the cancer is advanced and has spread, the prognosis may not be as good and there may be a higher risk of cancer recurrence.