The thymus is a small organ in the chest, just in front of the heart, that is part of the lymphatic system – the system basically responsible for removing toxins and waste from the body. They thymus is responsible for making T-cells, a special type of white blood cell that is important in fighting off infections. The thymus is special, because it only needs to produce those cells for a short period of time while a cat is young. As a cat ages the thymus is no longer needed because other parts of the body take over the job of fighting infections. Once the thymus isn’t needed anymore it will start to wither away.

A thymoma is a tumor that takes over the space the thymus used to occupy. A thymoma can be benign (not spreading) or malignant (spreading).


  • Coughing
  • Rapid breathing (tachypnea)
  • Shortness of breath (dyspnea)
  • Reduced appetite / anorexia with weight loss
  • Muscle weakness or muscle wasting
    • Commonly associated with high calcium levels (hypercalcemia)
    • Rarely associated with myasthenia – a special kind of muscle wasting disorder
  • Regurgitation
    • Bringing swallowed food back up to the mouth, an action commonly referred to as “vomiting” but involves whole food that hasn’t yet reached the stomach
    • This is a rare symptom that generally only occurs if the cat also has megaesophagus
  • Excessive urination (polyuria, PU) / excessive drinking (polydipsia, PD)
    • Common symptoms if the cat has hypercalcemia
  • Dermatitis


The treatment for thymoma is surgical removal of the tumor whenever possible. For tumors that cannot be surgically removed the treatment is radiation therapy and chemotherapy.

Additional treatment for the symptoms of thymoma may also be needed. Those treatments are dependent on the symptoms the cat has.


For the first year following surgical removal of the thymoma the cat should have physical exams and xrays every 3 months. After the first year the the monitoring can be moved to every 6 months.

For cats in chemotherapy the monitoring schedule will depend on the type and duration of chemotherapy.

Disease Information Sites

There are no sites devoted to thymoma that I could find. A general search will return a lot of basic information about the condition.

Support Groups

There are no specific support groups that I could find for thymoma. There is a good Feline Cancer group on Facebook that is active and has members familiar with thymoma.