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Posted Jul 02 2010 8:54am

Invasive Thymoma

          The thymus gland is in the upper part of the mediastinum (chest) behind the sternum and extending upwards into the root of the neck.  It is a small organ (reaching its maximum weight of about 1 ounce during puberty) that slowly decreases in size during adulthood and is gradually replaced by fat tissue.  During fetal development and childhood, the thymus produces white blood cells, called lymphocytes, that travel to lymph nodes (bean-sized collections of immune system cells) throughout the body.  There they help the immune system protect the body from infections.  The thymus contains two types of cells: epithelial cells and lymphocytes.  Thymic epithelial cells are the cells that line the thymus, and are the origin cells of thymoma and thymic carcinoma. If lymphocytes become malignant (cancerous), they can develop into lymphoma.  So, thymic cancer is a cancer of the thymus gland or thymic tissue.

          Although rare, thymomas are the most common type of thymic cancer. With fewer than 200 cases reported each, thymic cancer and thymic carcinoid tumors are very rare.  Thymic carcinomas tend to spread more rapidly and are more aggressive than thymomas. Taken together, thymic cancers represent only about 1.5% of all malignancies.  Thymic cancer is more common in the middle-aged and elderly; according to the National Cancer Institute (NCI), most patients diagnosed with these cancers are between 40 and 60 years of age.  Thymoma and thymic carcinoma affect men and women equally.  Thymic carcinoid tumors most frequently afflict men.  The cause of thymic cancer is unknown.  Cancer is caused when the normal mechanisms that control cell growth become disturbed, causing the cells to grow continually without stopping.  This is caused by damage to the DNA in the cell.  Thymic-related carcinomas and malignancies are difficult to diagnose, can be painful to treat and fraught with confusion and fear.  While great strides are being made in other areas of cancer research and treatment, thymic-related cancers and malignancies are relatively rare and often ignored by medical researchers.  For patients, this means that information is harder to find, treatment protocols are not solidly established and new drugs and treatments are not to be found.

          Approximately 30% of patients with thymoma or thymic carcinoma have no symptoms when it is diagnosed.  These are typically detected when doctors are looking for other things, during routine chest x-rays, for example.  If there are symptoms, they include:

  • Persistent Coughing
  • Chest pain
  • Upper airway congestion.
  • Muscle weakness
  • Fatigue
  • Shortness of breath
  • Arm or facial swelling
  • Difficulty swallowing
  • Anemia (low red blood cell count)
  • Increased risk of infection

If this type of malignancy is suspected, the physician will conduct a complete physical examination.  He or she may be able to feel a fullness in the lower neck region.  Routine blood tests may be performed.  Imaging studies are necessary because the symptoms of thymic cancer can be caused by many other diseases.  Thymic tumors can be identified by chest x- ray, magnetic resonance imaging (MRI) and computed tomography (CT).  About half of these tumors can be detected by a plain-film chest x-ray.

          The treatment for thymic cancer depends on the type and stage of cancer and the patient’s overall health.  Because thymic cancers are so rare, there are no defined treatment plans.  Treatment options include surgery, radiation therapy and/or chemotherapy.  Surgical removal of the tumor is the preferred treatment.  Surgery is often the only treatment required for stage I thymic cancers.  A treatment that is intended to aid the primary treatment is called adjuvant therapy.  For instance, chemotherapy may be used along with surgery to treat thymic cancer.  Stages II, III, and IV thymic cancers are often treated with surgery and some form of adjuvant therapy.  As of 2004, the preferred approach to thymic carcinoma is a combination of aggressive surgical treatment, chemotherapy using platinum-based compounds and radiation treatments. 

          The approximate five-year survival rates are 35% for thymic carcinomas and 60% for thymic carcinoids.  The five-year survival rates for thymomas are 96% for stage I, 86% for stage II, 69% for stage III and 50% for stage IV.  Thymomas rarely spread (metastasize) but thymic carcinomas frequently spread to distant organs.  Thymic carcinomas spread most often to the pleura, lung, local lymph nodes (bean-sized structures that contain lymphocytes), bone and liver.  Thymic carcinoid tumors commonly spread to local lymph nodes.  One should note that thymomas are prone to recurrence, even 10–15 years following surgery.  For thymomas, recurrence rates are drastically reduced and the five-year survival rates are drastically increased in patients who receive adjuvant radiation therapy.  Recurrence of thymic carcinoid tumors is common.  Thymomas are also associated with an increased risk of second malignancies.

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