ThymomaLast Updated: October 27, 2008 This section has been reviewed and approved by the Cancer.Net Editorial Board, 08/08 Overview
Thymoma is a type of cancer that begins in the thymus. The thymus is a small organ located under the sternum (breastbone) that makes white blood cells and is part of the lymph system. The lymph system is made up of thin tubes that branch out to all parts of the body. Its job is to fight infection and disease. The lymph system carries lymph, a colorless fluid containing white blood cells called lymphocytes. Lymphocytes fight germs in the body. B-lymphocytes (also called B-cells) make antibodies to fight bacteria, and T-lymphocytes (also called T-cells) kill viruses and foreign cells and trigger the B-cells to make antibodies. The thymus is involved in the production and maturation of T-lymphocytes. Groups of bean-shaped organs called lymph nodes are located throughout the body at different sites in the lymph system. Lymph nodes are found in clusters in the abdomen, groin, pelvis, underarms, and neck. In addition to the thymus, other parts of the lymph system include the spleen, which makes lymphocytes and filters blood, and the tonsils, located in the throat. Cancer begins when cells become abnormal and begin to grow uncontrollably. These cells for a mass of tissue, called a tumor. The thymus contains two main types of cells: epithelial cells and lymphocytes. Thymic epithelial cells are the cells that line the thymus, and this is where thymoma and a specific type of thymoma known as thymic carcinoma start. If lymphocytes become malignant (cancerous), they can develop into a type of cancer called lymphoma; see the Cancer.Net Guide to Hodgkin Lymphoma and Cancer.Net Guide to Non-Hodgkin Lymphoma for more information. Rarely, another type of tumor called a carcinoid tumor can develop in the thymus. Thymoma is generally a slow-growing tumor that does not usually spread outside of the thymus. Occasionally, it can spread to the pleura (lining of the lung). Less often, it can spread to other parts of the body. Thymic carcinoma (see Staging) can also be localized to the thymus, but is more likely to spread to the pleura and other parts of the body. Thymic carcinoma can also be more difficult to treat. In about 30% of people with thymoma, a condition called myasthenia gravis is also present. Myasthenia gravis comes from the Latin and Greek words meaning “grave muscular weakness.” It is an autoimmune disorder (a disorder caused by antibodies or T-cells that attack molecules, cells, or tissues of the organism producing them) that is characterized by fluctuating weakness of various muscle groups. Myasthenia gravis may affect any muscle that is under voluntary control, such as those that control eye movements, chewing, swallowing, coughing, and facial expression. Muscles that control breathing and movements of the arms and legs may also be affected. In addition to myasthenia gravis, people with thymoma can also have other associated syndromes, which as a group are called “paraneoplastic syndromes”, including pure red cell aplasia (severe anemia [low red blood cell count]) or hypogammaglobulinemia (low levels of immunoglobulins [antibodies] in the blood). Statistics Thymoma is rare. Approximately 90% of tumors of the thymus are thymoma. The remaining 10% are thymic carcinoma, carcinoid tumors, or lymphomas. Approximately 500 to 700 people in the United States are diagnosed with thymoma each year. Thymoma usually occurs in people between the ages of 40 and 60. Survival rates range depending on several factors, including the stage and classification of thymoma (see Staging). The five-year relative survival rate for thymic carcinoids and carcinomas is 60% and 35% respectfully. Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with thymoma. Source: American Cancer Society and the National Cancer Institute. Find out more about basic cancer terms used in this section. Risk Factors
A risk factor is anything that increases a person’s chance of developing cancer. Some risk factors can be controlled, such as smoking, and some cannot be controlled, such as age and family history. Although risk factors can influence the development of cancer, most do not directly cause cancer. Some people with several risk factors never develop cancer, while others with no known risk factors do. However, knowing your risk factors and communicating them to your doctor may help you make more informed lifestyle and health-care choices. There are no known risk factors for thymoma. Symptoms
People with thymoma may experience the following symptoms. Sometimes, people with thymoma do not show any of these symptoms. Or, these symptoms may be caused by a medical condition that is not cancer. If you are concerned about a symptom on this list, please talk to your doctor.
Diagnosis
Doctors use many tests to diagnose cancer and determine if it has metastasized (spread). Some tests may also determine which treatments may be the most effective. For most types of cancer, a biopsy is the only way to make a definitive diagnosis of cancer. If a biopsy is not possible, the doctor may suggest other tests that will help make a diagnosis. Imaging tests may be used to find out whether the cancer has metastasized. Your doctor may consider these factors when choosing a diagnostic test:
In addition to a physical examination, the following tests may be used to diagnose thymoma or thymic carcinoma: Biopsy. A biopsy is the removal of a small amount of tissue for examination under a microscope. Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis. The sample removed from the biopsy is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease). The type of biopsy performed will depend on the location of the cancer. A needle biopsy involves a long, thin needle that is inserted into the tumor to remove a piece of tissue. Sometimes, a core needle biopsy is performed, where a wider needle is used to take a cylindrical sample of the tumor. In some cases, depending on the location of the tumor, this procedure may be necessary for diagnosis. Also known as the Chamberlain procedure, this procedure is performed by making a two-inch incision about two inches to three inches from the breastbone and performing a biopsy of the tumor directly. Computed tomography (CT or CAT) scan. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient’s vein to provide better detail. Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. A contrast medium may be injected into a patient’s vein to create a clearer picture. X-ray. An x-ray is a picture of the inside of the body. For instance, a chest x-ray can help doctors determine if the cancer has spread to the lungs. Positron emission tomography (PET) scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient’s body and absorbed by the organs or tissues being studied. This substance gives off energy that is detected by a scanner, which produces the images. To learn more about what to expect during common diagnostic tests, read Cancer.Net: Tests and Procedures. To learn about the terms used in this section, read the Cancer.Net Feature: Cancer Terms to Know: Newly Diagnosed. Staging
Staging is a way of describing a cancer, such as where it is located, if or where it has spread, and if it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine the cancer's stage, so staging may not be complete until all the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis (chance of recovery). There are different stage descriptions for different types of cancers. There is no standard system for staging thymoma; however, the most commonly used system is called the Masaoka system. This system was developed in 1981, and it classifies thymoma into the following stages: Stage I: The cancer is limited to the thymus and the capsule that surrounds it. Stage II: The cancer has spread into fat surrounding the thymus or into the mediastinal pleura (the lining of the lung adjacent to the tumor). Stage III: The cancer has spread to other organs that are near the thymus, such as the lung, the pericardium (the sac around the heart), and the blood vessels. Stage IVA: The cancer has spread more extensively into the pleura (the lining of the lung) or the pericardium. Stage IVB: The cancer has spread to distant organs, or has spread through the vessels carrying blood or lymph. Noninvasive thymoma: Stage I thymoma may be referred to as noninvasive thymoma, when the tumor is limited to the thymus and has not invaded other tissues. Invasive thymoma: Stage II through stage IVB thymoma may be called invasive thymoma, when the tumor has invaded other tissues. Classification In addition to its stage, thymoma can be classified into different categories based on what the tumor cells look like under a microscope. The World Health Organization (WHO) developed the following system for classifying thymoma in 1999, and revised it in 2004: Type A thymoma. This type accounts for approximately 4% to 7% of all cases of thymoma, and is also referred to as spindle cell thymoma or medullary thymoma. The prognosis (chance of recovery) for people with type A thymoma is good, with a 15-year relative survival rate (percentage of patients who survive at least 15 years after the cancer is detected, excluding those who die from other diseases) near 100%. Type AB thymoma. Type AB thymoma, or mixed thymoma, accounts for approximately 28% to 34% of thymoma cases. Type AB thymoma is similar to type A; however, there are lymphocytes that are mixed in the tumor, and approximately 16% of cases are thought to be associated with myasthenia gravis. The prognosis for people with type AB thymoma is also good, with a 15-year relative survival rate of approximately 90%. Type B1 thymoma. Type B1 thymoma accounts for approximately 9% to 20% of thymoma cases, and is also known as lymphocyte-rich thymoma, lymphocytic thymoma, predominantly cortical thymoma, and organoid thymoma. This type of thymoma has a high concentration of lymphocytes in the tumor, but the cells of the thymus appear normal. Approximately 57% of type B1 thymoma cases are thought to be associated with myasthenia gravis. The prognosis for people with type B1 thymoma is also good, with a 20-year relative survival rate (percentage of patients who survive at least 20 years after the cancer is detected, excluding those who die from other diseases) of approximately 90%. Type B2 thymoma. Type B2 thymoma has a high concentration of lymphocytes, like type B1 thymoma; however, the thymus cells do not appear normal. Type B2 thymoma is also known as cortical thymoma and polygonal cell thymoma, and accounts for approximately 20% to 36% of all thymoma cases. About 71% of cases of type B2 thymoma are thought to be associated with myasthenia gravis. The 20-year relative survival rate for people with type B2 thymoma is approximately 60%. Type B3 thymoma. Type B3 thymoma is also known as epithelial thymoma, atypical thymoma, squamoid thymoma, and well-differentiated thymic carcinoma. It accounts for approximately 10% to 14% of thymoma cases. This type of thymoma has few lymphocytes, and the thymus cells look abnormal. About 46% of type B3 thymoma cases are thought to be associated with myasthenia gravis, and the 20-year relative survival rate is approximately 40%. Thymic carcinoma(or Type C thymoma). Thymic carcinoma is also referred to as Type C thymoma and is very aggressive. The cells in thymic carcinoma do not look like normal thymus cells, but like cancers in other organs of the body. Thymic carcinoma may start from a thymoma of another type that has transformed into a more aggressive tumor. This type of thymoma is often advanced when diagnosed. This tumor is classified into two categories: low grade (better prognosis) and high grade (more likely to grow and spread quickly). Low-grade thymic carcinoma includes basaloid, mucoepidermoid, and well-differentiated squamous cell types. High-grade thymic carcinoma includes anaplastic/undifferentiated, clear cell, poorly differentiated squamous cell, sarcomatoid, and small cell/neuroendocrine types. Most people with thymic carcinoma do not have associated myasthenia gravis. The five-year relative survival rate of people with thymic carcinoma is 38%. The 10-year relative survival rate of people with thymic carcinoma is 28%. Cancer survival statistics should be interpreted with caution. These estimates are based on data from thousands of cases of this type of cancer in the United States, but the actual risk for a particular individual may differ. It is not possible to tell a person how long he or she will live with thymoma. Treatment
The treatment of thymoma depends on the size and location of the tumor, whether the cancer has spread, and the person’s overall health. In many cases, a team of doctors will work with the patient to determine the best treatment plan. Surgery Surgery is the most common treatment for early stage thymoma. This is often performed through a median sternotomy, where the sternum is split, which allows the full removal of the thymoma and some additional tissue surrounding the tumor. Surgery is often the only treatment needed for early stage thymoma. Later stage thymoma may include surgery to “debulk” (remove as much of the tumor as possible) the tumor, when a complete surgical removal is not possible. Debulking surgery may provide some relief of symptoms. If the thymoma has spread to the lining of the lung, surgery may also include a pleurectomy (removal of the lung lining) or removal of a portion of the lung. Radiation therapy Radiation therapy is the use of high-energy x-rays or other particles to kill cancer cells. The most common type of radiation treatment is called external-beam radiation, which is radiation given from a machine outside the body. When radiation treatment is given using implants, it is called internal radiation therapy (or brachytherapy). Side effects may include fatigue, mild skin reactions, difficulty swallowing, upset stomach, and loose bowel movements. Most side effects go away soon after treatment is finished. External-beam radiation therapy can be used alone, following surgery, or in combination with chemotherapy in the treatment of thymoma. Radiation therapy is usually recommended after the thymoma has been removed surgically in patients with later stage disease. Chemotherapy Chemotherapy is the use of drugs to kill cancer cells. Systemic chemotherapy uses drugs to target cancer cells throughout the body. The side effects of chemotherapy depend on the individual, the type of drug used, and the dose, but can include fatigue, risk of infection, nausea and vomiting, and hair loss. These side effects usually go away once treatment is finished. The most common chemotherapy drugs in the treatment of thymoma are doxorubicin (Adriamycin, Rubex), cisplatin (Platinol), cyclophosphamide (Cytoxan, Neosar), etoposide (VePesid, Etopophos, Toposar), and ifosfamide (Ifex, Holoxan). The common combinations used for the treatment of thymoma include cyclophosphamide, doxorubicin, and cisplatin, or etoposide and cisplatin. These chemotherapy combinations are sometimes used to shrink the tumor before surgery if the thymoma is more advanced. Chemotherapy may also be used for people who have stage IVB/advanced thymoma or recurrent thymoma (cancer that comes back after treatment) that is not surgically removable. The medications used to treat cancer are continually being evaluated. Talking with your doctor is often the best way to learn about the medications prescribed for you, their purpose, and their potential side effects or interactions with other medications. Learn more about your prescriptions through Cancer.Net’s Drug Information Resources, which provides links to searchable drug databases. To learn about the terms used in this section, read the Cancer.Net Feature: Cancer Terms to Know: During Treatment. Clinical Trials Resources
Doctors and scientists are always looking for better ways to treat patients with thymoma. A clinical trial is a way to test a new treatment to prove that it is safe, effective, and possibly better than a standard treatment. Patients who participate in clinical trials are among the first to receive new treatments, such as new chemotherapy before they are widely available. However, there is no guarantee that the new treatment will be safe, effective, or better than a standard treatment. Patients decide to participate in clinical trials for many reasons. For some patients, a clinical trial is the best treatment option available. Because standard treatments are not perfect, patients are often willing to face the added uncertainty of a clinical trial in the hope of a better result. Other patients volunteer for clinical trials because they know that finding new drugs and other therapies is the only way to make progress in treating thymoma. Even if they do not benefit directly from the clinical trial, their participation may benefit future patients with thymoma. To join a clinical trial, patients must complete a learning process known as informed consent. During informed consent, the doctor should list all of the patient’s options, so the person understands how the new treatment differs from the standard treatment. The doctor must also list all of the risks of the new treatment, which may or may not be different from the risks of standard treatment. Finally, the doctor must explain what will be required of each patient in order to participate in the clinical trial, including the number of doctor visits, tests, and the schedule of treatment. Learn more about clinical trials, including patient safety, phases of a clinical trial, deciding to participate in a clinical trial, questions to ask the research team, and links to find cancer clinical trials. Side Effects
Cancer and its treatment can cause a variety of side effects. However, doctors have made major strides in recent years in reducing pain, nausea and vomiting, and other physical side effects of cancer treatments. Many treatments used today are less intensive but as effective as treatments used in the past. Doctors also have many ways to provide relief to patients when such side effects do occur. Fear of treatment side effects is common after a diagnosis of cancer, but it may be helpful to know that preventing and controlling side effects is a major focus of your health-care team. Before treatment begins, talk with your doctor about possible side effects of the specific treatments you will be receiving. The specific side effects that can occur depend on a variety of factors, including the type of cancer, its location, the individual treatment plan (including the length and dosage of treatment), and the person’s overall health. Ask your doctor which side effects are most likely to happen (and which are not), when side effects are likely to occur, and how they will be addressed by the health-care team if they do happen. Also, be sure to communicate with the doctor about side effects you experience during and after treatment. For more information on the most common side effects of cancer and different treatments, along with ways to prevent or control them, visit Cancer.Net’s section on Managing Side Effects, based on ASCO’s curriculum. In addition to physical side effects, there may be psychosocial (emotional and social) effects as well. Learn more about the importance of addressing these needs in Cancer.Net’s section on Caring for the Whole Patient For more information on late effects or long-term side effects, please read the After Treatment section or talk with your doctor. After Treatment
After treatment for thymoma ends, talk to your doctor about developing a follow-up care plan. Follow-up care depends on the stage of thymoma treated. Regular visits to the doctor and follow-up CT scans are often recommended, particularly for more advanced stages of thymoma. Follow-up physical examinations and regular CT scans may be part of lifetime care for some people. There may be some risk for a second malignancy (another type of cancer) particularly in people who have received radiation therapy. In these situations, there is a small risk of a new type of cancer developing many years later in the area treated by radiation therapy. People recovering from thymoma or thymic carcinoma are encouraged to follow established guidelines for good health, such as maintaining a healthy weight, not smoking, eating a balanced diet, and having recommended cancer screening tests. Talk with your doctor to develop a plan that is best for your needs. Moderate physical activity can help rebuild your strength and energy level. Your doctor can help you create an appropriate exercise plan based upon your needs, physical abilities, and fitness level. Learn more about Healthy Living After Cancer To learn about the terms used in this section, read the Cancer.Net Feature: Cancer Terms to Know: After Treatment. Current Research
Research for thymoma is ongoing. The following advances may still be under investigation in clinical trials and may not be approved or available at this time. Always discuss all diagnostic and treatment options with your doctor. Drug combinations. Drugs used in chemotherapy work in different ways to stop tumor cells from dividing so they stop growing or die. Combining more than one drug may help to eliminate more tumor cells. The combination of carboplatin (Paraplatin) and paclitaxel (Taxol) is being studied for the treatment of advanced thymoma. New agents.These therapies are being explored in clinical trials:
Questions to Ask the Doctor
Regular communication with your doctor is important in making informed decisions about your health care. Consider asking the following questions of your doctor:
Patient Information Resources
Foundation for Thymic Cancer Research Rare Cancer Alliance National Organization for Rare Disorders (NORD) View all of Cancer.Net's Patient Information Resources. |
