Thymic carcinoma is a cancer that starts in the outer layers of the thymus gland. It is a very rare form of cancer, but it can be aggressive and difficult to treat.

The American Cancer Society (ACS) estimates there are about 400 new cases of thymic cancer each year in the United States. The overall 5-year survival rate of thymic carcinoma is 71%.

This article explains the differences between thymic carcinoma and thymoma, as well as exploring the symptoms, causes, and risk factors of thymic carcinoma. It also describes how doctors diagnose thymic carcinoma and what treatment options a person with thymic cancer can expect.

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The National Cancer Institute (NCI) defines thymic carcinoma as a rare cancer of the thymus. The NCI describes it as an aggressive cancer that can spread quickly to other parts of the body. There is also a high risk of it returning after treatment.

The thymus is a gland that lies in the chest, just behind the breastbone. It is part of the immune system and makes lymphocytes, a type of white blood cell.

Thymic carcinoma starts in the epithelial cells, or the outer layer, of the thymus. Thymomas also start in these cells, but these tumors are less aggressive and are less likely to spread beyond the thymus.

Doctors group thymic carcinoma and thymoma together using the term thymic epithelial tumors (TETs). Thymic carcinoma accounts for approximately 20% of TETs, according to the NCI.

The ACS explains that both of these tumors are very rare in the U.S., occurring at a rate of 1.5 cases in every million people each year.

What is thymic carcinoma?

Thymic carcinoma is a thymic cancer that starts in the epithelial cells of the thymus, a small organ in the upper chest.

Many people with thymic carcinoma do not have any symptoms of the condition, according to the ACS. When people experience symptoms, they can include:

As the ACS explains, the tumor can sometimes press on the superior vena cava, an important vein carrying blood from the head, chest, and arms to the heart. This is called superior vena cava syndrome (SVC syndrome). It can cause swelling in the face, neck, and chest, headache, and dizziness. SVC syndrome requires immediate medical attention.

No one knows exactly what causes thymic carcinoma, but doctors have identified some risk factors. The ACS says that aging plays a part. It is more common in people ages 70 years and older than in children or young adults.

Thymic carcinoma can be difficult to diagnose as the symptoms are similar to those of other conditions, according to the Genetic and Rare Diseases Information Center (GARD). Doctors begin the process of diagnosis with a physical exam and a review of the person’s medical history.

After this, doctors may recommend X-rays and scans, including CT, PET, and MRI scans. They may perform a biopsy to remove cells from the thymus for microscopic examination as well.

Staging thymic carcinoma

Once doctors diagnose thymic carcinoma, the person has more tests to establish how far the cancer has advanced and whether it has spread to other parts of the body. Thymic carcinoma spreads quickly and has usually spread by the time of diagnosis, according to the NCI.

Doctors use a staging system to work out the best treatment options for thymic carcinoma. The ACS explains this as the TNM system, which looks at the size of the original tumor (T), whether it has spread, or metastasized, to the lymph nodes (N), and whether it has spread to other organs (M).

Each of these categories may also contain a number or letter. For example, T1N0M0 shows that the original tumor is small (T1), has not spread into the lymph nodes (N0), and has not metastasized into other organs (M0). A doctor will explain what the numbers and letters mean, as they will be different for each person with thymic carcinoma.

Doctors use the TNM system to assign the cancer an overall stage of 1 to 4. The higher the number, the farther the cancer has spread. Doctors also use the Masaoka-Koga staging system for thymic carcinomas.

Learn more about cancer staging.

Doctors tailor their treatment plans individually for each person with thymic carcinoma. According to the ACS and NCI, the healthcare team may recommend:

  • Surgery: This treatment removes the thymus gland and any parts of nearby organs or blood vessels that contain signs of thymus cancer. If doctors cannot remove the whole gland, they may try to remove as much of the tumor as possible. “Debulking” is the term for this process.
  • Radiation therapy: This treatment may reduce the risk of the cancer coming back in the original site. Doctors may also use radiation to reduce the size of the tumor in people with SVC syndrome or in people who do not have surgery.
  • Chemotherapy: This drug therapy is an option for advanced stage tumors. Doctors may also recommend chemotherapy to reduce the tumor’s size before surgery to remove it.
  • Hormone therapy: People with thymic cancer may receive octreotide, a drug that mimics the hormone somatostatin.
  • Targeted therapy: This treatment involves drugs that target cancer cells more directly than chemotherapy and radiation. Targeted therapies work by blocking certain processes that cancer cells need to grow and spread.
  • Clinical trials: Due to the rarity of the disease, doctors are still developing the best treatment options, including specific combinations of drugs. Taking part in a clinical trial gives people with thymic cancer access to the latest treatments under investigation.

Survival rates estimate the likelihood of a person with a particular cancer being alive after a fixed period of time (usually 5 years). The ACS uses a system that groups the cancer into one of three categories:

  • Localized: It has not spread beyond the thymus.
  • Regional: The cancer is growing into nearby organs.
  • Distant: The cancer is widespread in the body.

The latest ACS figures show:

Stage5-year survival rate

Many factors affect the outlook of thymic carcinoma. Someone with this type of cancer should discuss the outlook with their doctor, who will consider their overall health, stage of cancer, and treatment options, including participation in a clinical trial.

Thymic carcinoma is a rare and aggressive form of cancer that begins in the thymus. It spreads quickly and may be difficult to treat in later stages or after recurrence. However, medical research is ongoing, and treatments are evolving. Treatments under clinical evaluation include biological therapies and combinations of different drugs.