Thymoma is a cancer that develops in the cells on the surface of the thymus gland (the gland that creates T lymphocytes, or T cells, which are vital to a person’s immune system). Thymomas are relatively uncommon, although they are the primary type of cancer to develop in the thymus.
Most thymomas are slow-growing, and very few ever spread outside of the thymus. While some oncologists classify thymomas as either malignant (cancerous) or benign (noncancerous), most prefer to treat every thymoma as if it could potentially be malignant. Survival rates are generally favorable, especially when the tumors are diagnosed early and properly treated by highly specialized oncologists like those in Moffitt’s Thoracic Oncology Program.
Thymoma can cause a number of symptoms, many of which affect the respiratory system. This isn’t surprising, given that thymoma develops in the chest, behind the sternum. Some of the most common symptoms of thymoma include:
- Difficulty breathing
- Shortness of breath
- A persistent, dry cough
- Chest pain (often manifesting as a dull, aching pain)
- Double vision
- Difficulty swallowing
- Muscle weakness
- Swelling within the face and hands
- Frequent infections
It’s important to note that thymoma affects each person differently. In fact, while some thymoma patients experience a wide array of symptoms, others don’t notice anything at all. You should also remember that many of the symptoms of thymoma could also indicate something much less serious—such as pneumonia or a chest cold—so you should make an appointment with a medical provider before assuming the worst.
Thymoma Causes & Risk Factors
Researchers are still working to determine the exact cause of thymoma, as well as risk factors that can make certain individuals more susceptible to this malignancy. With that being said, studies suggest that certain conditions affecting the immune system—such as hypogammaglobulinemia, lupus, myasthenia gravis, red cell aplasia, rheumatoid arthritis, sarcoidosis and ulcerative colitis—could make someone more likely to develop thymoma. However, because many individuals with these conditions never develop thymoma, there’s no conclusive link to this malignancy.
Types of Thymoma
Thymoma can be classified into different types based on the kind of cell found within the tumor. These types include:
- Type A thymoma (also known as medullary thymoma, predominantly epithelia thymoma or spindle cell thymoma)
- Type AB thymoma (also known as mixed thymoma or small polygonal type thymoma)
- Type B1 thymoma (also known as lymphocyte-rich thymoma, lymphocytic thymoma, organoid thymoma or predominantly cortical thymoma)
- Type B2 thymoma (also known as cortical thymoma or mixed lymphocytic and epithelial thymoma)
- Type B3 thymoma (also known as atypical thymoma, epithelial thymoma, squamoid thymoma or well-differentiated thymic carcinoma)
- Metaplastic thymoma (also known as byphasic thymoma, low-grade metaplastic carcinoma or thymoma with pseudosarcomatous stroma)
- Micronodular thymoma with lymphoid stroma (also known as micronodular thymoma with lymphoid B cell hyperplasia)
It should be noted that it can sometimes be very difficult to identify the exact type of thymoma, and certain cases can’t even be identified as one specific type. What’s more, the type of thymoma present typically has little to no influence on a patient’s prognosis—staging is the more important factor in this regard.
A thymoma diagnosis typically requires several tests. If a physician suspects thymoma, he or she will usually begin by ordering one or more diagnostic imaging tests, which may include:
- Computed tomography (CT) scans
- Magnetic resonance imaging (MRI)
- Positron emission tomography (PET) scans
If the results of these imaging tests suggest the presence of thymoma, the next step will likely be to perform a biopsy. After a physician removes a small sample of the tumor (or in some cases, the entire tumor), a pathologist will examine the sample under a microscope to determine whether the cells are cancerous.
Unlike other types of cancers that use a single staging system, thymoma can be staged using two different models: the Masaoka system (which focuses on how far the thymoma has already spread based on imaging tests and tumor analyses) and the World Health Organization’s histological classification system (which focuses on the appearance of the thymoma cells).
Under the Masaoka system, thymoma can be classified into the following stages:
- Stage 1 - Thymoma will be classified as Stage 1 if the tumor has not yet spread to the thymus’s outer layer.
- Stage 2A - In this stage, the tumor has already started to grow into the thymus’s outer layer or into nearby tissues and membranes.
- Stage 2B - Once the tumor has grown into the thymus’s outer layer or into nearby tissues and membranes, thymoma will be classified as Stage 2B.
- Stage 3 - Thymoma will be classified as Stage 3 if the tumor has started growing into nearby organs and tissues.
- Stage 4A - In this stage, the tumor has grown extensively into nearby tissues and membranes.
- Stage 4B - Once the tumor has metastasized (spread to distant organs within the body), thymoma will be classified as Stage 4B.
Under the World Health Organization’s histological classification system, a tumor will be classified using the following labels:
- Class A
- Class B1
- Class B2
- Class B3
- Class C
Thymoma treatment often involves a combination of the following methods:
- Radiation therapy
Thymoma treatment plans will vary from one patient to another depending on factors such as the stage of the cancer, the size of the tumor and the patient’s age and overall health. Physicians will also consider how the patient has responded to previous treatments.
A thymoma patient’s prognosis will depend on a variety of factors, including:
- The stage of the cancer at the time the patient is diagnosed - Cases where the cancer has not yet metastasized generally have better outcomes.
- The type of cells within the tumor - While staging has significantly more influence over outcomes, cell types (histology) also have some impact.
- The patient’s age and overall health - Because young, otherwise healthy patients are often eligible for more therapies than their older counterparts, they tend to have better outcomes.
It’s important to note that as researchers continue to learn more about how thymoma tumors respond to treatment, outcomes are steadily improving.
At Moffitt Cancer Center, we take a unique approach to treating thymoma. We offer a comprehensive range of therapies for thymus cancers, including surgery, radiation therapy, chemotherapy and clinical trials, all in one convenient location. More importantly, however, we tailor each patient’s thymoma treatment plan to meet his or her specific needs. This gives us the opportunity to:
- Account for individual factors, such as the stage and cellular makeup of the cancer and the patient’s age, when deciding which treatments to recommend
- Determine if newer, more innovative therapies (accessible through our robust clinical trial program) offer more potential benefits and fewer potential risks than other currently used thymoma treatment options
- Help each patient maintain his or her quality of life throughout the duration of treatment
Additionally, patients don’t just work with one oncologist when they come to Moffitt; every individual is cared for by a multispecialty team of thymoma experts. This means that radiation oncologists, medical oncologists, surgeons, pulmonologists and other skilled medical professionals all work together to develop a patient’s treatment plan. And, this team meets every week to review the patient’s response to treatment, making modifications as necessary to achieve the best possible outcomes.