What is thymus cancer?

Thymus cancer starts in the cells of the thymus. A cancerous (malignant) tumour is a group of cancer cells that can grow into and destroy nearby tissue. It can also spread (metastasize) to other parts of the body. Cancerous tumours of the thymus are rare.

The thymus is a small gland in the top part of the chest between the lungs and under the breastbone. It makes T cells (T lymphocytes) that travel throughout the body to help fight infection, disease and foreign substances. The thymus also makes hormones and other substances to help T cells develop and keep the immune system working properly.

Diagram of the location of the thymus
Diagram of the location of the thymus

Cells of the thymus sometimes change and no longer grow or behave normally. These changes may lead to non-cancerous (benign) tumours such as thymic cysts and thymolipomas.

In some cases, changes to thymus cells can cause thymus cancer. Most often, thymus cancer starts in the epithelial cells of the thymus. These types of thymus cancer are called thymoma and thymic carcinoma.

Thymus cancer can also start in other types of cells, such as thymic neuroendocrine tumours (NETs).

Expert review and references

The thymus

The thymus is a gland in the upper part of the chest, just behind the breastbone (sternum) and between the lungs. The thymus is part of the endocrine system and the lymphatic system.

Cancerous tumours of the thymus

Malignant tumours of the thymus are cancerous growths that have the potential to spread (metastasize) to other parts of the body. Most thymus tumours are found in the anterior (front) mediastinum, near the left lung and in front of or to the side of the pericardium.

Classification of thymoma and thymic carcinoma

Thymoma and thymic carcinoma can be divided into groups based on what the cancer cells look like under a microscope. Along with the stage, this classification helps your healthcare team plan your treatment and predict future outcomes (your prognosis).

Non-cancerous tumours of the thymus

A benign tumour is a non-cancerous growth that does not spread (metastasize) to other parts of the body and is usually not life-threatening. Benign tumours of the thymus are rare. Types include thymic cyst, thymolipoma and thymic hyperplasia.

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