Thymoma

Causes and risk factors

The exact cause of thymoma is not known, but there are some factors that may increase the risk. These include:

• The breed: Labradors and Golden Retrievers appear to be more likely to develop thymomas than other breeds.
• Age: Most dogs with thymomas are between nine and ten years old.
• Gender : There is no difference between male and female dogs in the incidence of thymoma.

Symptoms

The symptoms of thymomas depend on the size and location of the tumor. A thymoma can press on neighboring organs such as the heart, lungs, esophagus and blood vessels, causing various symptoms. The most common symptoms include

• shortness of breath
• lethargy
• loss of appetite
• weight loss
• cough
• Difficulty swallowing
• Swelling in the head, neck and chest area
• Weakness or paralysis of the muscles

Some dogs with thymomas can also suffer from paraneoplastic syndromes, which are diseases that are triggered by the tumor but are not directly related to it. The best-known paraneoplastic syndrome in dogs with thymomas is myasthenia gravis, an autoimmune disease that leads to impaired signal transmission between nerves and muscles. The result is muscle weakness, which is particularly noticeable in the face, jaw, eyelids and limbs.

Diagnosis

To diagnose a thymoma, the vet must perform a thorough clinical examination and order various tests. These include:

• Blood tests: These may show signs of anemia, inflammation, infection or hypercalcemia (elevated blood calcium levels).
• X-rays: These can show the size and shape of the tumor in the chest.
• Ultrasound examination: This can assess the structure and blood flow of the tumor.
• Biopsy: This is necessary to take a tissue sample from the tumor and examine it under a microscope. This allows the vet to determine the type and stage of the tumor.

The staging of thymomas is based on the extent to which the tumor has spread to the surrounding tissue and lymph nodes or other organs. There are four stages of thymoma:

• Stage I: The tumor is completely encapsulated and has not spread.
• StageII: The tumor has broken through the capsule or has grown into the surrounding fatty tissue.
• StageIII : The tumor has infiltrated the neighboring organs such as the heart or lungs or has invaded the large blood vessels.
• StageIV: The tumor has metastasized to the lymph nodes or other organs such as the liver or spleen.

Treatment

The treatment of thymomas depends on the stage, size, location and general condition of the dog. The main treatment options are:

• Surgery: this is the preferred method to remove the tumor if it is operable. Surgical excision can significantly improve the dog's survival time and quality of life. However, surgery can also be associated with risks and complications, such as bleeding, infection or damage to surrounding organs.
• Chemotherapy: This is a drug therapy designed to inhibit the cell division of the tumor. Chemotherapy can be used alone or in combination with surgery, especially for advanced or metastasized thymomas. However, chemotherapy can also cause side effects such as nausea, vomiting, hair loss or bone marrow suppression.
• Radiotherapy: This is a therapy that uses high-energy radiation to kill the tumor cells. Radiotherapy can be used alone or in combination with surgery or chemotherapy, especially for inoperable or residual thymomas. However, radiotherapy can also cause side effects such as skin irritation, hair loss or pulmonary fibrosis.