Thymic Carcinoma

Thymic carcinoma is a rare and aggressive form of cancer that develops in the thymus, a small gland located behind the breastbone that helps your body fight infections. Unlike its less aggressive counterpart thymoma, thymic carcinoma grows quickly and is more likely to spread to other parts of the body, making it more challenging to treat.

Table of contents

• What is thymic carcinoma?
• Location and function of the thymus
• Who is affected?
• Signs and symptoms
• How is it diagnosed?
• Treatment options
• Outlook and survival

What is thymic carcinoma?

Thymic carcinoma is a rare cancer that starts in the cells covering the outside surface of the thymus gland. Along with thymoma, it belongs to a group of cancers called thymic epithelial tumors (TETs), which means they develop from the epithelial cells of the thymus^[1].

Even though thymic carcinoma and thymoma both start in the same type of cell, they behave very differently. The cancer cells in thymic carcinoma do not look like normal thymus cells when examined under a microscope. They grow much more quickly than thymoma cells and are far more likely to spread to other parts of your body, a process called metastasis^[2].

Thymic carcinoma accounts for about one in every five thymic epithelial tumors, making it less common than thymoma but significantly more difficult to treat^[2]. It is considered the more aggressive form of thymic cancer^[5].

Location and function of the thymus

The thymus is a small organ that sits in the upper part of your chest, just behind your breastbone and above your heart. It is positioned in an area called the anterior mediastinum, which is the front part of the space between your lungs^[2].

• Thymus gland
• Chest (thorax)
• Mediastinum

The thymus plays an important role in your body’s defense system. It is part of the lymph system and produces special white blood cells called T-lymphocytes or T-cells. These cells help protect your body against infections by recognizing and fighting off harmful bacteria and viruses^[1].

Who is affected?

Thymic carcinoma is extremely rare. Only about 400 people in the United States are diagnosed with all forms of thymic cancer combined each year, and thymic carcinoma represents only a portion of these cases^[1].

This cancer most commonly affects adults between the ages of 40 and 75. A study looking at cases in the United States from 2001 to 2015 found that the highest number of cases occurred in people between 70 and 74 years old. The disease is also more common in males than in females^[5]. In the United States, most people diagnosed with thymic cancers have Asian or Pacific Islander heritage^[1].

Unlike thymoma, which is strongly linked to autoimmune conditions like myasthenia gravis, thymic carcinoma is rarely associated with paraneoplastic syndromes—conditions where the immune system mistakenly attacks healthy cells^[5].

Signs and symptoms

Most people with thymic carcinoma do not have symptoms in the early stages of the disease. The cancer is often discovered by chance during a chest X-ray or other imaging test done for an unrelated reason^[2].

When symptoms do occur, they usually happen because the tumor has grown large enough to press on nearby organs or structures in the chest. The development of symptoms typically indicates that the cancer is at an advanced stage^[5].

Common symptoms include^[1]:

• A cough that does not go away
• Chest pain or a feeling of pressure on the chest
• Shortness of breath
• Difficulty swallowing
• A hoarse voice

In some cases, the tumor can press on or block a large vein in the chest called the superior vena cava, which carries blood from the upper body to the heart. This can cause a serious condition called superior vena cava syndrome. Signs of this condition include^[1]:

• Swelling in the face, neck, and upper body
• Swelling in the arms and hands
• Visible veins in the upper part of the body
• Shortness of breath
• Cough
• Dizziness and headaches
• Fatigue

How is it diagnosed?

Diagnosing thymic carcinoma involves a combination of imaging tests, physical examination, and tissue analysis. Because many cases are found without symptoms, the process often begins when a chest X-ray reveals a mass in the front part of the chest^[2].

Your doctor will start with a physical exam and review of your medical history. They will check for general signs of health and ask about any symptoms you may be experiencing^[2].

Several imaging tests may be used to get a detailed look at the tumor^[3]:

• Chest X-ray to identify a mass in the chest
• CT scan (computed tomography scan) to create detailed pictures of the chest area
• MRI scan (magnetic resonance imaging) for additional detailed images
• PET scan (positron emission tomography) to see if the cancer has spread

The most definitive way to diagnose thymic carcinoma is through a biopsy, where a small sample of tissue is removed and examined under a microscope by a specialist called a pathologist. The biopsy is considered the gold standard for diagnosis and helps distinguish thymic carcinoma from thymoma and other types of tumors^[5].

A biopsy may be done before surgery using a technique called fine needle aspiration, or it may be performed during surgery with immediate examination by the pathologist^[5]. It is important to rule out other cancers that may have spread to the thymus, as they can look similar under the microscope^[5].

Treatment options

Treatment for thymic carcinoma depends on the stage of the cancer, meaning how far it has spread. The main goal is to remove the tumor completely if possible^[5].

Surgery is the primary treatment for thymic carcinoma. When the entire tumor can be removed, it offers the best chance for controlling the disease. Even when complete removal is not possible, surgeons may perform debulking surgery to remove as much of the tumor as they can^[5].

After surgery, additional treatments are usually needed. If the surgeon was unable to remove all of the cancer or if there is a high risk that the cancer will come back, radiation therapy may be recommended. Radiation uses high-energy beams to kill cancer cells^[5].

For thymic carcinoma, treatment after surgery often includes one of the following^[7]:

• Radiation therapy alone
• Chemotherapy followed by radiation therapy

Chemotherapy uses medicines to kill cancer cells throughout the body. It may be given before surgery to shrink the tumor, or after surgery to kill any remaining cancer cells. For cancer that has spread to other parts of the body, chemotherapy is the main treatment^[5].

Because thymic carcinoma is rare and can be difficult to treat, patients may be offered the chance to participate in clinical trials. These are research studies testing new treatments that may be more effective than current options^[1].

Outlook and survival

Thymic carcinoma is associated with a poorer outlook compared to thymoma. It is often diagnosed at advanced stages, and the cancer has a tendency to come back after treatment. Recurrence following treatment is common^[5].

The five-year survival rate for patients with inoperable, locally advanced thymic carcinoma is 36%. For patients whose cancer has spread to distant parts of the body (metastatic disease), the five-year survival rate is 24%^[24].

The stage at which the cancer is diagnosed plays a major role in determining outcomes. At the time of diagnosis, spread of cancer outside the chest cavity is estimated to occur in less than 7% of cases^[5].

Because thymic tumors can recur many years after initial treatment, long-term follow-up care is essential. Regular check-ups with your healthcare team help ensure that any recurrence is detected early, when it may be easier to treat^[18].