Tumors of the Thymus in Cats

Key takeaways

Thymic tumors are abnormal growths of tissues of the thymus gland, and are rare in cats.

  • The most common types are lymphoma and thymoma
  • These tumors can be classified as invasive (spread to other areas around the thymus) or non-invasive (well-localized and contained)
  • Thymic tumors are not often metastatic and are more likely to be non-invasive
  • Symptoms can be non-specific but include breathing difficulties, weight loss, difficulty swallowing, and exercise intolerance
  • Diagnosis is through diagnostic imaging and biopsy of the tumor
  • Treatment options include surgical removal of the tumor, chemotherapy, radiation, and corticosteroids
  • Prognosis is generally good and recurrence is low in cases of non-invasive thymoma tumors.
  • Thymic lymphoma carries a more guarded prognosis
  • Invasive thymic tumors and concurrent myasthenia gravis have poor prognoses
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A closer look: Tumors of the Thymus in Cats

The thymus is a small glandular structure in front of the heart. It is important in the development and maturation of T-lymphocytes, which are essential components of the body's immune system.

While thymic tumors in general are rare in cats, lymphoma and thymoma are the most common types seen.

Thymic tumors have an overall fair prognosis, depending on the invasiveness and metastasis (spread) of the tumor. If other conditions develop, especially myasthenia gravis, prognosis can be poorer as this can lead to aspiration pneumonia.

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Risk factors

In areas with high incidence of feline leukemia virus (FeLV), mediastinal lymphoma is most common in young (2-3 years), FeLV- positive cats. There may be a predisposition for Siamese and male cats.

Thymoma is a disease of older cats with a median age at diagnosis of 12 years. Domestic shorthair cats appear to be predisposed.

Some cats develop symptoms affecting the skin.

In some cases, thymus tumors can cause myasthenia gravis in cats.

Myasthenia gravis may lead to aspiration pneumonia, which can be life threatening.

Possible causes

The direct cause of thymus tumors is currently unknown. Mediastinal lymphoma is prominent in younger cats which are positive for feline leukemia virus (FeLV) and there is evidence of some breed predisposition for thymus tumors. At this time a specific genetic or environmental cause has yet to be identified.

Main symptoms

Symptoms are nonspecific, vague, and may not be clinically apparent.

Testing and diagnosis

After a physical examination and medical history, a number of tests can be done to confirm diagnosis of a thymus tumor:

  • Biopsy
  • Diagnostic imaging
  • Blood work

Steps to Recovery

Treatment depends on the type of tumor. Chemotherapy is the primary treatment for lymphoma of the thymus, with radiation also utilized in some rare cases. Surgical excision with adjunctive chemotherapy is usually indicated for thymoma.

Supportive therapy includes:

  • Post- operative oxygen therapy
  • Anti-emetics
  • Appetite stimulants
  • Corticosteroids for concurrent myasthenia gravis

Prognosis with a successful surgery for non-invasive thymoma is good. The rate of recurrence is low (10-20%) and in the case of recurrence, the second surgery is often effective. If the tumor is invasive or has metastasized, prognosis is poorer. If aspiration pneumonia is present, the prognosis is very poor.

In cases of thymic lymphoma, prognosis is poor, with a median survival time of around 200 days.


Feline leukemia vaccinations help decrease the incidence of some types of thymic tumors. Monitoring of overall health and changes in behavior can allow for the condition to be caught earlier.

Thymus tumors are not contagious.

Is Tumors of the Thymus in Cats common?

Thymus tumors are uncommon in cats.

Typical Treatment

  • Surgery
  • Chemotherapy
  • Radiation
  • Supportive care

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