Thymoma

What are thymomas?

Thymomas are tumors of the thymus gland that originate from the epithelial cells. In the majority of cases they are benign, grow slowly and remain confined to the gland. Thymomas are rarely malignant. The cells then divide and multiply rapidly and invade the surrounding tissue. The most aggressive form of tumor in this group is thymus carcinoma. In principle, any benign thymoma can become malignant in the course of time.

The thymus gland is a lymphatic organ that sits behind the upper breastbone and plays an important role in immune defense. From puberty onwards, the thymus tissue regresses and in adulthood consists only of fatty tissue and a small amount of thymus tissue. Thymomas are tumors of the mediastinum – the space between the two lungs. The mediastinum also contains the heart, the esophagus and the large blood vessels such as the aorta.

The causes of thymoma are unknown in many cases. However, thymoma often occurs in conjunction with other diseases, such as myasthenia gravis or Sjögren’s syndrome – both of which are autoimmune diseases.

Thymomas usually go unnoticed in the early stages. If they grow and press on neighboring structures, such as the trachea or esophagus, they can cause symptoms such as coughing, shortness of breath and chest pain. Doctors often discover tumors in the thymus gland by chance during a radiological examination.

The treatment depends on the type, size and spread of the tumor. The treatment of first choice is always an operation in which the thymoma is completely removed.

Depending on the stage (classification according to international criteria such as size, cell type, cross-border growth or spread to neighboring lymph nodes), other treatment modalities such as chemotherapy or radiation are used. The cure rate for thymomas is very high, but also depends on the stage of the disease.

Thymomas – frequency and age

Thymomas are very rare overall. Experts have calculated that they only occur in 0.13 out of 100,000 people per year. Nevertheless, they are among the most common tumors in the mediastinum. They are responsible for around 50 percent of all tumors there. In three quarters of cases, thymomas are benign – in around a third, the growth is malignant.

In principle, tumors of the thymus gland can occur at any age and in both sexes equally. However, the disease peaks between the ages of 50 and 60. At this age, benign thymomas are often associated with myasthenia gravis – a nerve and muscle weakness. However, other autoimmune diseases also occur concomitantly, for example Sjögren’s syndrome (a disease of the lacrimal and salivary glands), polymyositis (a disease of the connective tissue) or rheumatoid arthritis, which destroys the joints.

Thymomas: often caused by other diseases

The causes of malignant thymomas are unknown. The starting point is always a cell whose genetic material (DNA) changes – the cell degenerates and can divide and multiply unchecked. This is the case with all cancers. But why the cell mutates often remains a mystery.

Benign thymomas, on the other hand, often occur together with another disease. These include, for example:

• Myasthenia gravis: An autoimmune disease associated with neurological disorders and muscle weakness. In 20 to 40 percent of cases, myasthenia gravis is accompanied by a thymoma.
• Polymyositis: An inflammatory disease of the muscles that is an autoimmune disease.
• Sjögren’s syndrome: An autoimmune disease in which the immune system attacks the lacrimal and salivary glands and later also other organs.
• Rheumatoid arthritis: An autoimmune disease in which the body’s own defenses are directed against the joints and gradually destroy them.
• Thyroiditis: Inflammation of the thyroid gland, which is also often caused by an autoimmune disease (Hashimoto’s thyroiditis).
• Lupus erythematosus: This autoimmune disease can damage many organs and organ systems.
• Hypogammaglobulinemia: A disease of the immune system that repeatedly leads to infections. Those affected have a lack of antibodies.
• Anemia – thymomas are also frequently found here.

Symptoms: Thymomas often go unnoticed

Thymomas do not necessarily cause symptoms. Around 30 percent of all patients experience no symptoms and the disease remains undetected. Thymomas are often discovered by chance during a radiological examination. Symptoms usually only develop when the thymoma grows and reaches a certain size – then it presses on neighboring organs such as the trachea or esophagus.

The following signs may indicate thymoma:

• Feeling of pressure behind the breastbone
• Pain in the chest area
• A cough that won’t go away
• Shortness of breath or stridorwhen the thymoma presses on the windpipe
• Difficulty swallowing if the thymoma presses on the esophagus
• Hoarseness, if the so-called brachial nerve is impaired
• Cardiac dysfunction if the thymoma is compressing the heart
• Upper influence congestion: The venous return flow from the head and arms no longer functions properly because the superior vena cava is compressed. Symptoms include congested and dilated veins in the neck, head and arms as well as headaches or a feeling of pressure in the head and neck.
• Muscle weakness, rapid fatigability, decrease in physical performance

Thymoma: Diagnosis

Thymomas are often discovered by chance during an X-ray examination that takes place for another reason. Otherwise, diagnostics always begin with a discussion about your medical history, during which we ask you a few questions (medical history), for example:

• What are your symptoms?
• When did the symptoms first occur and how intense are they?
• Do you have any known illnesses, for example autoimmune diseases such as myasthenia gravis, rheumatoid arthritis or Sjögren’s syndrome?
• Are you taking any medications? If yes: Which ones and since when?

This is followed by a physical examination, which includes palpation of the chest and neck area. This allows changes to be detected, such as tumors or enlarged lymph nodes. Further information is provided by imaging techniques such as:

• X-ray examination of the chest (chest X-ray)
• Computed tomography (CT): An X-ray examination in which radiologists create detailed cross-sectional images – this allows thymomas to be detected with a high degree of certainty. It also shows the location and size of the thymoma and whether it has already grown into neighboring structures. Sometimes the thymus gland is enlarged, but there is no thymoma – this is also shown by CT.
• Magnetic resonance imaging (MRI = magnetic resonance imaging): This method works with strong magnetic fields and can also reveal a thymoma.
• Blood and urine tests: By determining hormones, we try to rule out other types of tumors that may also be located in the chest area.
• Octreotide scintigraphy: We determine whether or not the hormone somatostatin accumulates in the tumor tissue. This is later important for the question of whether hormone therapy with somatostatin is possible.

To diagnose most types of cancer, we usually take a tissue sample (biopsy) from the suspected area. The cells are then analyzed under a microscope by a pathologist in the laboratory. This makes it possible to determine with absolute certainty whether the cells are benign or malignant. However, it is often difficult to remove tissue from thymomas because the thymus gland is located in an area that is difficult to access. In these cases, the tissue is only analyzed after the tumor has been removed during an operation. In certain situations, for example if the imaging information does not guarantee complete surgical removal of the tumor, the tumor is pretreated with radiation.

Thymomas – classification by stage

Depending on the size and spread of the thymoma, it is divided into different stages (staging according to Masaoka-Koga):

• Stage I: The tumor is still confined to the thymus gland and the thymus capsule – it has not yet broken through them.
• Stage IIa: The tumor has only penetrated the capsule to a small extent.
• Stage IIb: The tumor has left the thymus gland and spread to the surrounding fatty tissue up to the pleura. It is fused with the pleura or the pericardium.
• Stage III: The tumor has invaded neighbouring organs, e.g. pericardium, lungs, large vessels or certain nerves.
• Stage IVa: The tumor has spread to the pleura of the heart or lungs.
• Stage IVb: Cancer cells have spread to other organs via the bloodstream and lymphatic channels – distant metastases form.

The choice of treatment and prognosis then depend on these stages. The lower the stage (lower the number), the more favorable it is. There is also the classification of the World Health Organization (WHO), which classifies thymomas according to different cell types (histologically). According to this classification, there are thymoma types A, AB, B1, B2 and B3. Thymus carcinoma is referred to as type C. The aggressiveness of the tumor increases from type A (most benign behavior) to type C (most malignant behavior). There is also a further tumor classification according to the TNM classification. This represents a new classification that is easy to apply and helpful for treatment decisions.

The WHO classifies almost all thymomas – regardless of the nature of the cells – as malignant. The reason is that all thymomas – even apparently benign ones – can become malignant over time. There are only a few exceptions, such as microscopic thymoma or fibrolipoadenoma. Put simply, thymomas can be distinguished from the very malignant thymus carcinoma.

Thymomas: prevention, early detection, prognosis

As with many types of cancer, the causes of thymoma are often unknown. Therefore, you cannot really prevent thymoma. There are also no special measures for early detection. As a general rule, always visit us promptly if you experience symptoms. Rapid diagnosis and timely treatment improve the prognosis and chances of recovery. This also applies to many other types of cancer.

Course and prognosis of thymoma

The course and prognosis of thymomas are generally good – even in the case of malignant thymomas. However, the stage and spread of the tumor are always decisive. The earlier the thymoma is discovered and treated, the more favorable the prognosis. In most cases, the tumor in the thymus gland can be completely removed by surgery. Sometimes this is followed by other treatments that improve the chances of recovery, such as chemotherapy or radiotherapy. Early stages of thymoma have a very good early and long-term prognosis after complete removal.

Thymomas: treatment consists of surgery

Doctors from a wide range of specialist disciplines are always involved in the treatment of thymomas, for example from thoracic surgery, radiology, oncology and pathology. They work closely together and discuss each case individually in tumor conferences. The individual, patient-specific treatment strategy is also determined there. Which therapy is suitable always depends on the stage and spread of the thymoma. A combination of several therapy modalities is also possible.