Thymomas are typically slow-growing tumors that affect your thymus gland. If one spreads to nearby organs like the lungs and heart, it can make treatment more challenging, but early detection can improve outlooks.

A thymoma is a cancerous tumor in your thymus gland, a small gland in your chest that helps produce immune cells.

As thymomas grow, they spread (metastasize) to nearby tissues and can travel to organs throughout the body. At this point, the tumor is known as a metastatic thymoma.

Metastatic thymomas are more challenging to treat because cancerous cells intermingle with healthy cells in vital organs like your heart and lungs. Destroying cancer cells can mean destroying healthy cells along with them. This is even more challenging when cancerous cells spread far beyond the thymus throughout the body.

Read on to learn about where thymomas usually metastasize, how fast a thymoma can spread, and how a metastatic thymoma can be diagnosed and treated.

Your thymus gland is next to several major organs. So, if a thymoma metastasizes, it can spread to several locations.

Locations include your:

These organs are also surrounded by tissues and blood vessels that thymomas can grow into as well, including the:

  • pericardium, a tissue sac that keeps your heart in place and protects it from infections
  • pleura, a membrane around the lungs full of fluid that protects and lubricates the lungs
  • superior vena cava, a major vein that brings blood into the heart to give it oxygen again before it’s pumped back out into your body
  • phrenic nerve, a major nerve that helps control your breathing and diaphragm movement

Thymomas do not spread very quickly. Compared to other types of cancers, they’re considered slow-growing tumors.

Some research suggests that the size of a thymoma can affect how likely — and quickly — it can spread beyond the thymus gland.

Data in 2018 from 1,272 people with thymomas found that large tumors were more likely to spread and less likely to result in successful treatment.

The researchers noted that tumors larger than 90 millimeters (around 3.5 inches) were more likely to require treatments like chemotherapy.

Sometimes, you’ll experience symptoms that may be early signs of a thymoma, including:

Early treatment and diagnosis can help keep a thymoma from spreading.

But, not everyone has symptoms when they have a thymoma. If the thymoma has spread, doctors may need to use a variety of tests to find the cancer and where it’s spread to.

Some tests used to detect metastatic thymoma include:

What stage is metastatic thymoma?

Thymus cancer is categorized into four stages. Doctors usually classify metastatic thymomas as stage 4, although they may start to spread in earlier stages.

  • Stage 1: The thymoma is contained to your thymus gland and the capsule around the thymus.
  • Stage 2: The thymoma has started to spread outside the thymus capsule into the tissues around the heart, known as the pericardium.
  • Stage 3: The thymoma starts to spread to nearby organs like the lungs, esophagus, and trachea, along with major blood vessels around the heart and lungs.
  • Stage 4: The thymoma may have spread into the heart, lungs, and lymph nodes. In this stage, cancerous cells are more likely to travel and spread throughout the body in other organs.

Treatment for metastatic thymoma can be more challenging because it involves other healthy tissues and organs.

Some of the possible treatment options may also be done in combination for better results, including:

  • a thymectomy to remove the thymus and any cancerous tissue around it
  • radiation therapy to reduce the size of tumors using high-energy rays
  • chemotherapy to kill cancer cells using medications injected into the body
  • hormone therapy to block hormones that may be allowing cancer cells to grow
  • metabolic treatments, such as a ketogenic diet, to reduce some of the substances in your body that can help cancer cells grow

If these therapies don’t fully treat your thymus cancer, a doctor may also recommend you join a clinical trial. These trials aren’t guaranteed to treat metastatic thymomas but can sometimes have promising results from cutting-edge treatments.

According to the American Cancer Society (ACS), the 5-year relative survival rate for people with thymus cancer that has spread to distant parts of the body is 38%.

The 5-year relative survival rate is the percentage of people with the disease who are still alive 5 years after diagnosis compared to people who don’t have the disease.

But the figure from the ACS also includes thymic carcinoma, a more aggressive form of thymic cancer. According to the National Cancer Institute, the 10-year disease-free survival ranges from 28–100% depending on the type of cancer cells in the thymoma.

Resources for support

The Foundation for Thymic Cancer Research provides a list of support groups for people with thymomas. They also host many other education and outreach tools so you can connect with a community that understands what you’re going through.

The University of California, San Francisco and City of Hope both offer various resources for people with thymomas.

Thymomas grow slowly, and metastatic thymomas are rare. Doctors can treat or successfully remove most thymomas before they metastasize in other organs. Early treatment is critical to reduce the risk of a thymoma spreading.

Contact a healthcare professional if you notice any new symptoms that concern you, such as trouble breathing and a persistent cough, or find any lumps around your chest.