Thymoma Malignant

Malignant thymoma is a rare cancer that grows in the thymus, a small gland located in your chest behind your breastbone. While it most often does not cause symptoms in the early stages, it has the ability to spread and invade nearby tissues, making early detection and treatment crucial.

Table of contents

• What is malignant thymoma?
• Where is the thymus located and what does it do?
• Types of thymic tumors
• Who is affected?
• Signs and symptoms
• Associated autoimmune conditions
• How is it diagnosed?
• Treatment options
• What to expect
• Follow-up care

What is malignant thymoma?

Malignant thymoma is a cancer that develops in the thymus gland, a small organ located in your upper chest. The term “malignant” means that these tumors have the ability to invade nearby tissues and spread to other parts of your body^[1]. All thymomas are now considered to have malignant potential, though their behavior can vary greatly^[2].

Thymoma and thymic carcinoma are both types of thymic epithelial tumors (TETs) because they develop from the epithelial cells that line the surface of the thymus^[2]. While both start in the same type of cell, they behave differently. Thymomas tend to grow slowly and rarely spread beyond the thymus. Thymic carcinomas, on the other hand, grow more quickly and are more likely to spread to other parts of your body, making them harder to treat^[1][2].

Where is the thymus located and what does it do?

Your thymus is a small gland that sits in the upper chest behind your breastbone and between your lungs^[2]. It is part of your lymphatic system, which helps your body fight infections^[2].

• Upper chest (anterior mediastinum)
• Behind the breastbone (sternum)
• Between the lungs

The thymus plays an essential role in your immune system by making special white blood cells called T-lymphocytes or T-cells. These cells help your body fight infections^[1][2]. The thymus grows until puberty and then slowly shrinks and is replaced by fatty tissue as you age^[3].

Types of thymic tumors

There are two main types of cancer that can form in the thymus^[8]:

Thymoma is the more common type. The cancer cells look similar to normal thymus cells, grow slowly, and rarely spread beyond the thymus. Different types of thymoma are classified by how the cells look under a microscope, with types ranging from A to B3^[8].

Thymic carcinoma is much rarer, accounting for about one in every five thymic epithelial tumors^[2]. The cancer cells look very different from normal thymus cells. They grow more quickly and have usually spread to other parts of the body by the time the cancer is found. About 20% of all thymic epithelial tumors are thymic carcinomas^[3].

The 15-year survival rate is 12.5% in patients with invasive thymomas and 47% in patients with noninvasive thymomas^[3].

Who is affected?

Thymomas and thymic carcinomas are rare cancers. Only about 400 people in the United States are diagnosed each year^[1]. They are the most common tumors of the anterior mediastinum, accounting for approximately 20% of all mediastinal tumors^[3].

These cancers most commonly affect adults between 40 and 75 years of age^[1]. They commonly occur between the fourth and sixth decades of life^[3]. In the United States, most people diagnosed have Asian or Pacific Islander heritage^[1]. There is no known difference in rates between men and women^[3].

The cause of thymomas and thymic carcinomas is not known, and there are no known risk factors for developing these cancers^[3].

Signs and symptoms

Most people don’t have symptoms in the early stages of thymoma or thymic carcinoma. These cancers are often found by chance during a chest x-ray done for another reason^[2][4]. When symptoms do occur, they usually happen because the tumor is pressing on nearby organs in your chest^[1].

Common symptoms include^[1][2]:

• Chest pain or a feeling of pressure on your chest
• A cough that won’t go away
• Shortness of breath
• Trouble swallowing
• Hoarse voice
• Loss of appetite
• Weight loss

Tumors can sometimes block or squeeze the large veins that carry blood to your heart, called the vena cava. This compression can cause a very serious condition known as superior vena cava syndrome^[1]. If this happens, you may experience^[1][4]:

• Swelling in your face, neck, and upper chest, sometimes with a bluish color
• Swelling in your arms and hands
• Visible veins in the upper part of your body
• Shortness of breath
• Cough
• Headaches
• Dizziness or feeling lightheaded
• Fatigue

Associated autoimmune conditions

Thymomas are commonly associated with autoimmune paraneoplastic syndromes. These are conditions where your body’s immune system mistakenly attacks not only cancer cells but also normal, healthy cells^[2]. About 30 to 40% of patients with thymoma experience symptoms related to these conditions^[3].

The most common autoimmune conditions associated with thymoma are^[1][2]:

Myasthenia gravis is the most common condition linked to thymoma. It affects your nerves and muscles, causing muscle weakness. Between 30% and 65% of patients with thymoma have been diagnosed with myasthenia gravis^[15].

Pure red cell aplasia (PRCA) is a blood disorder where your bone marrow doesn’t make enough red blood cells, causing anemia^[1].

Hypogammaglobulinemia (also called Good syndrome) is an immune system disorder where your body doesn’t make enough antibodies to fight disease and prevent infections^[1]. It occurs in 5% to 20% of thymoma cases^[15].

Other autoimmune conditions that appear less often include^[1]:

• Polymyositis
• Lupus erythematosus
• Rheumatoid arthritis
• Thyroiditis
• Sjögren syndrome

Thymic carcinomas are rarely associated with these autoimmune conditions^[15].

How is it diagnosed?

Diagnosing thymoma and thymic carcinoma begins with a physical exam and a review of your medical history and symptoms^[4]. Your doctor will then arrange for you to have several tests^[2].

Common tests include^[2]:

A chest x-ray may be the first test that suggests a problem. Many thymomas are found during a chest x-ray done for another reason^[2].

A CT scan (computed tomography scan) creates detailed pictures of the inside of your chest. It is one of the main tests used to examine the thymus^[4].

An MRI scan (magnetic resonance imaging) uses magnets and radio waves to create detailed images of your body’s soft tissues^[4].

A PET scan (positron emission tomography) may be used to see if the cancer has spread to other parts of your body^[4].

Blood tests may be done to check for signs of autoimmune conditions associated with thymoma^[4].

A biopsy involves taking a small sample of tissue from the tumor to examine under a microscope. The only way to positively diagnose thymoma is through a biopsy^[4]. However, you might not need a biopsy if your doctor thinks it’s very likely that you have thymus gland cancer based on your scans and blood test results^[8].

Treatment options

Treatment for malignant thymoma depends on the stage of the cancer, the type of tumor, and whether the surgeon can completely remove it^[8][12]. A team of doctors and other professionals discuss the best treatment and care for you. They are called a multidisciplinary team^[8].

Surgery is the main treatment for thymoma and gives the best chance of curing the cancer if possible^[8][11]. Complete surgical removal of the tumor is the cornerstone of successful therapy^[11]. The goal is to remove the entire thymus gland along with the tumor.

Radiation therapy may be used after surgery if the surgeon was not able to completely remove the cancer, or if there is a high risk of the cancer coming back^[8][12].

Chemotherapy uses drugs to kill cancer cells. Thymomas are sensitive to chemotherapy^[14]. It may be used before surgery to shrink the tumor, after surgery to reduce the risk of the cancer returning, or as the main treatment for cancers that cannot be removed by surgery^[11][14]. Common chemotherapy regimens include combinations of platinum-based drugs like cisplatin with other medications^[14].

For advanced or unresectable disease, a multimodality approach combining chemotherapy, surgery, and radiation therapy is often recommended^[14]. Studies have shown that aggressive multimodal treatment can be effective and may be curative in locally advanced, unresectable malignant thymomas^[14].

Clinical trials may offer access to new treatments that are being tested. Your doctor can discuss whether a clinical trial might be appropriate for you^[1].

Treatment for thymic carcinoma usually involves chemotherapy after surgery, or chemotherapy followed by radiation therapy^[8]. Because thymic carcinoma is more aggressive and more likely to have spread by the time it is diagnosed, it is more difficult to treat than thymoma^[2].

What to expect

The outlook for patients with malignant thymoma varies depending on several factors, including the stage of the cancer, the type of tumor, and whether it can be completely removed by surgery^[2].

Thymomas that grow slowly and rarely spread beyond the thymus generally have a better prognosis. The 15-year survival rate is 47% in patients with noninvasive thymomas^[3]. However, invasive thymomas that have spread to nearby tissues have a lower survival rate, with a 15-year survival rate of 12.5%^[3].

Thymic carcinomas are more aggressive and harder to treat. The 5-year survival rate is 36% for patients with inoperable, locally advanced carcinoma and 24% for patients with metastatic thymoma and thymic carcinoma^[15].

Deaths related to thymomas usually occur from complications such as cardiac tamponade or other cardiorespiratory problems^[3].

Follow-up care

Regular follow-up with your doctor is very important after treatment for thymoma. Thymomas can come back up to 20 years after treatment, which is why lifetime follow-up is recommended^[19]. Regular doctor’s appointments increase the chance that if the cancer returns, it will be found earlier when it is easier to treat^[19].

Living with the possibility that the cancer might come back for such a long time can be very stressful. You can use your follow-up visits to discuss your concerns and ask questions^[19]. Report any signs or symptoms that may suggest the cancer has returned as soon as possible^[19].

People who have been diagnosed with thymoma are at a greater risk of developing a second cancer. This risk appears to be the same whether you are treated with surgery or radiation therapy, or have a history of myasthenia gravis^[19]. The second cancers that can develop after thymoma include non-Hodgkin lymphoma and soft tissue sarcoma^[19].

If fear of the cancer coming back is stopping you from moving forward, you may want to talk to a counselor or join a cancer survivor support group^[19]. Look for ways to help you cope, manage stress, and improve your health through activities like meditation, staying physically active, and eating a healthy diet^[19].