Thymic cancer is any one of several different types of tumors that have originated within the thymus gland.
The thymus is located in the upper chest just below the neck. It is a small organ that produces certain white blood cells before birth and during childhood. These white blood cells are called lymphocytes and are an important part of the body's immune system. Once released from the thymus, lymphocytes travel to lymph nodes where they help to fight infections. The thymus gland becomes smaller in adulthood and is gradually taken over by fat tissue.
Three cell types of the thymus can give rise to cancer. The epithelial cells that make up the outer covering of the thymus can become cancerous resulting in thymic carcinoma and thymoma . When the lymphocytes in the thymus or lymph nodes become cancerous, the resulting cancers are called Hodgkin's disease or non-Hodgkin's lymphomas . A third, less common, cell type in the thymus is called Kulchitsky cells (neuroendocrine cells). These cells release chemical messengers called hormones. Cancer that originates from Kulchitsky cells is called thymic carcinoid tumors. Another type of thymic cancer, thymolipoma, is composed of thymic tissue and fatty 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 carcinoma tends to spread and is more aggressive than thymoma.
Thymic cancer is more common in the middle-aged and elderly. Thymoma and thymic carcinoma affect men and women equally. Thymic carcinoid tumors most frequently afflict men.
Causes and symptoms
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 tumors are not usually evident until the enlarged thymus presses on the windpipe (trachea) or blood vessels, which cause symptoms. The symptoms of thymic cancer will vary depending on what type of cancer is present. Symptoms of any thymic tumor may include: shortness of breath, swelling of the face, coughing, and chest pain.
Thymic carcinoid tumors can release hormones that may cause symptoms. Symptoms of thymic carcinoid tumors may also include red and warm skin, (flushing), diarrhea , and asthma.
Approximately 40% of the patients diagnosed with thymoma have no symptoms. The signs and symptoms of thymoma are vast and are related to the many disorders caused by thymoma. The most common conditions related to thymoma (paraneoplastic syndromes ) are red cell aplasia, myasthenia gravis , and hypogammaglobulinemia. These conditions are autoimmune diseases, those in which the body mounts an attack against certain normal cells of the body. Symptoms of thymoma may also include:
- muscle weakness (especially in the eyes, neck, and chest, causing problems with vision, swallowing, and breathing)
- shortness of breath
The physician will conduct a complete physical exam. 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).
A biopsy may be performed, in which a small sample of the tumor is removed and examined under the microscope. However, because of the risk of "seeding" cancerous cells, biopsies are not routinely performed. Because other tumors can lie in the region of the thymus, thymic cancer can be diagnosed only by identification of the cells that make up the tumor. There are a few different methods for biopsy of a thymic tumor. For a mediastinoscopy , a wand-like lighted camera (endoscope) and special instruments are passed through a small cut in the lower neck. The surgeon can see the tumor on a monitor and can cut off small samples for microscopic analysis. Mediastinoscopy is performed under general anesthesia. Alternatively, a needle biopsy will be taken in which a long needle is passed through the skin and into the tumor. Fine needle biopsy uses a thin needle and larger-core needle biopsy uses a wider needle. Needle biopsies may be performed in conjunction with computed tomography imaging.
Patients who are having difficulty breathing may have a bronchoscopy performed to examine the wind pipe. An endoscope, in this case a bronchoscope, is inserted through the mouth and into the windpipe. The physician will look for tumors and may perform biopsies.
The treatment team for thymic cancer may include a hematologist, pulmonologist, immunologist, oncologist, thoracic surgeon, cardiologist, radiation oncologist, nurse oncologist, psychiatrist, psychological counselor, and social worker.
Clinical staging, treatments, and prognosis
There is more than one type of staging system for thymic cancer but the Masaoka system is used most often. This staging system was developed for thymoma, however, it is sometimes used to stage the other thymic cancers as well. Thymic carcinoma is graded (low or high) based on the cell type present in the tumor. Thymoma is categorized into four stages (I, II, III, and IV) which may be further subdivided (A and B) based on the spread of cancerous tissue. The Masaoka staging system is as follows:
- Stage I. The thymoma lies completely within the thymus.
- Stage II. The thymoma has spread out of the thymus and invaded the outer layer of the lung (pleura) or nearby fatty tissue.
- Stage III. The thymoma has spread to other neighboring tissues of the upper chest including the outer layer of the heart (pericardium), the lungs, or the heart's main blood vessels.
- Stage IVA. The thymoma has spread throughout the pericardium and/or the pleura.
- Stage IVB. The thymoma has spread to organs in other parts of the body.
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.
Thymic cancer may be treated by surgically removing (resecting) the tumor and some of the nearby healthy tissue. Removal of the entire thymus is called a thymectomy. Surgery on the thymus is usually performed through the chest wall by splitting open the breast bone (sternum), a procedure called a median sternotomy. When complete removal of the tumor is impossible, the surgeon will remove as much of the tumor as possible (debulking surgery, sub-total resection). In these cases, If the tumor has spread, surgery may include removal of other tissues such as the pleura, pericardium, blood vessels of the heart, lung, and nerves.
Radiation therapy uses high-energy radiation from x rays and gamma rays to kill the cancer cells. Radiation given from a machine that is outside the body is called external radiation therapy. Radiation therapy is often used as adjuvant therapy following surgery to reduce the chance of cancer recurrence. Radiation may be used to kill cancer cells in cases in which the tumor was only partially removed. It may be used before surgery to shrink a large tumor. Radiation therapy is not very effective when used alone, although it may be used alone when the patient is too sick to withstand surgery.
The skin in the treated area may become red and dry and may take as long as a year to return to normal. Radiation to the chest may damage the lung causing shortness of breath and other breathing problems. Also, the tube that goes between the mouth and stomach (esophagus) may be irritated by radiation causing swallowing difficulties. Fatigue, upset stomach, diarrhea, and nausea are also common complaints of patients having radiation therapy. Most side effects go away about two to three weeks after radiation therapy has ended.
Chemotherapy uses anticancer drugs to kill the cancer cells. The drugs are given by mouth (orally) or intravenously. They enter the bloodstream and can travel to all parts of the body. Chemotherapy may be given before surgery to shrink a tumor, which is called neoadjuvant therapy. Thymic tumor cells are very sensitive to anticancer drugs, especially cisplatin , doxorubicin , and ifosfamide . Generally, a combination of drugs is given because it is more effective than a single drug in treating cancer.
The side effects of chemotherapy are significant and include stomach upset, nausea and vomiting , appetite loss (anorexia) , hair loss (alopecia ), mouth sores, and fatigue. Women may experience lose of appetite (anorexia) vaginal sores, menstrual cycle changes, and premature menopause. There is also an increased chance of infections.
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.
Thymomas are prone to recurrence, even 10 to 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.
Alternative and complementary therapies
Although alternative and complementary therapies are used by many cancer patients, very few controlled studies on the effectiveness of such therapies exist. Mind-body techniques such as prayer, biofeedback, visualization, meditation, and yoga, have not shown any effect in reducing cancer but they can reduce stress and lessen some of the side effects of cancer treatments. Gerson, macrobiotic, orthomolecular, and Cancell therapies are ineffective treatments for cancer.
Clinical studies of hydrazine sulfate found that it had no effect on cancer and even worsened the health and well-being of the study subjects. One clinical study of the drug amygdalin (Laetrile) found that it had no effect on cancer. Laetrile can be toxic and has caused deaths. Shark cartilage, although highly touted as an effective cancer treatment, is an improbable therapy that has not been the subject of clinical study. Although the results are mixed, clinical studies suggest that melatonin may increase the survival time and quality of life for cancer patients.
Selenium, in safe doses, may delay the progression of cancer. Laboratory and animal studies suggest that curcumin, the active ingredient of turmeric, has anticancer activity. Maitake mushrooms may boost the immune system, according to laboratory and animal studies. The results of laboratory studies suggest that mistletoe has anticancer properties, however, clinical studies have not been conducted.
For more comprehensive information, the reader should consult the book on complementary and alternative medicine published by the American Cancer Society listed in the Resources section.
Coping with cancer treatment
The patient should consult his or her treatment team regarding any side effects or complications of treatment. Many of the side effects of chemotherapy can be relieved by medications. Patients should consult a psychotherapist and/or join a support group to deal with the emotional consequences of cancer and its treatment.
As of early 2001, there were two active clinical trials studying thymic cancer, both sponsored by the National Cancer Institute. One trial (#E-1C99) was studying the effectiveness and toxicity of carboplatin and paclitaxel on thymic cancers. This study was open to patients with invasive, recurrent, or metastatic thymoma or thymic carcinoma. The other (#E-1C97) was studying the effectiveness and toxicity of octreotide both with and without prednisone for metastatic or recurrent thymoma. The National Cancer Institute web site has information on these and other studies. Patients should consult with their treatment team to determine if they are candidates for these or any other ongoing studies.
Because there are no known risk factors for the development of thymic cancer there are no preventive measures. However, there may be an association between thymic cancer and exposure of the chest to radiation.
Damage to the lungs and/or esophagus caused by radiation therapy to the upper chest is a concern. Biopsy runs the risk of seeding tumor cells to other parts of the body.
See Also Thoracotomy
Bruss, Katherine, Christina Salter, and Esmeralda Galan, eds. American Cancer Society's Guide to Complementary and Alternative Cancer Methods. Atlanta: American Cancer Society, 2000.
Cameron, Robert, Patrick Loehrer, and Charles Thomas. "Neo plasms of the Mediastinum." In Cancer: Principles & Practice of Oncology, DeVita Vincent T., Samuel Hell man, and Steven Rosenberg, eds. Philadelphia: Lippincott Williams & Wilkins, 2001, pp. 1019-36.
Giaccone, Giuseppe. "Treatment of Thymoma and Thymic Carcinoma." Annals of Oncology 11, suppl. 3 (2000): 245-6.
American Cancer Society. 1599 Clifton Rd. NE, Atlanta, GA 30329. (800) ACS-2345. <http://www.cancer.org>.
"Thymus Cancer." American Cancer Society. November 1999. 29 April 2001. 6 July 2001 <http://www3.cancer.org/cancerinfo>.
Belinda Rowland, Ph.D.
—A treatment that is intended to aid the primary treatment. Adjuvant treatments for thymic cancer are radiation therapy and chemotherapy.
—A type of white blood cell that is found in the thymus.
—Radiation therapy or chemotherapy used to shrink a tumor before surgical removal of the tumor.
—A set of symptoms that is associated with cancer but is not directly caused by the cancer.
—The outer covering of the lungs.
QUESTIONS TO ASK THE DOCTOR
- What type of thymic cancer do I have?
- What stage of cancer do I have?
- Has the cancer spread?
- What is the five year survival rate for patients with this type of cancer?
- Will you perform a biopsy?
- What type of biopsy will you perform?
- What is the risk of seeding cancerous cells during a biopsy?
- What are my treatment options?
- What are the risks and side effects of these treatments?
- What medications can I take to relieve treatment side effects?
- Are there any clinical studies underway that would be appropriate for me?
- What effective alternative or complementary treatments are available for thymic cancer?
- How debilitating is the treatment? Will I be able to continue working?
- What is the chance that the cancer will recur?
- What are the signs and symptoms of recurrence?
- What can be done to prevent recurrence?
- How often will I have follow-up examinations?