Thymoma natural history

If left untreated, thymoma may progress to invade the mediastinum and the surrounding structures. Depending on the stage of the tumor at the time of diagnosis, the prognosis may vary. The prognosis is generally regarded as good. Common complications of thymoma include the pressure effect of the mass itself, autoimmune diseases, and rarely, progression to malignancy.

• One-third of the tumors are discovered because of an associated autoimmune disorder.
• The most common of these autoimmune disorders is myasthenia gravis: 10 – 15% of patients with myasthenia gravis have thymoma. And 30 – 45% of patients with thymoma have myasthenia gravis.
• Patients with thymoma demonstrate a tendency for local mediastinal recurrence and pleural ‘‘droplet’’ recurrence presumably caused by mediastinal pleural invasion after resection.^[1]

Complications associated with thymoma include:

• Pressure effect associated with thymoma (sometimes presenting as superior vena cava syndrome)
• Autoimmune diseases associated with thymoma (myasthenia gravis and pure red cell aplasia)
• Thymic malignancy of unknown etiology
• Rarely (approximately 7% of cases), metastasis to pleura, bones, liver, or brain^[2]

The most common complications of radiotherapy are:^[1]

• Pulmonary fibrosis
• Pericarditis
• Myelitis

The most common complications of thymectomy are:

• Complications of the procedure, such as:
  • Bleeding
  • Infection
  • Damage to other organs
  • Nerve injuries (bilateral phrenic nerve injury)
  • Respiratory failure
• Recurrence has been described 10 to 20 years after removal of the primary lesion, necessitating long-term follow up.
• Live attenuated vaccines, such as yellow fever vaccine, may have adverse effects after thymectomy due to an inadequate T-cell response.

The complications of taking thymic biopsy include:

• Pneumothorax
• Mediastinitis

The prognosis of thymoma depends on the following:

• Location of the tumor
• Stage of the tumor

• The prognosis is much worse for stage III or IV thymoma as compared to stage I and II tumors
• Patients with stage III and IV tumors may nonetheless survive for several years with appropriate oncological management

• Resectability of the tumor
• Patient’s general health
• Primary diagnosis vs. recurrence
• Histologic type (mixed histologic type is associated with the worst prognosis)^[1]

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