Thymus cancer

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Stages of thymus cancer

Staging describes or classifies a cancer based on how much cancer there is in the body and where it is when first diagnosed. This is often called the extent of cancer. Information from tests is used to find out the size of the tumour, which parts of the organ have cancer, whether the cancer has spread from where it first started and where the cancer has spread. Your healthcare team uses the stage to plan treatment and estimate the outcome (your prognosis).

Two staging systems are used to classify thymoma and thymic carcinoma – the modified Masaoka system and the TNM system. There are 4 stages of thymus cancer in each system. Often the stages 1 to 4 are written as the Roman numerals I, II, III and IV. Generally, the higher the stage number, the more the cancer has spread. Talk to your doctor if you have questions about staging.

When describing the stage, doctors may use the words local, regional or distant. Local means that the cancer is only in the thymus and has not spread to other parts of the body. Regional means close to the thymus or around it. Distant means in a part of the body farther from the thymus.

Find out more about staging cancer.

Modified Masaoka staging

The modified Masaoka staging system is the one most commonly used for thymoma.

Stage 1

The tumour is within the thymus.

Stage 2

The tumour has grown through the thymus capsule (the connective tissue covering the outside of the thymus) and may have grown into surrounding fat or is attached to nearby pleura.

Stage 3

The tumour has grown into nearby organs or tissues, such as the lungs, the large blood vessels near the heart or the pericardium (the sac that surrounds the heart).

Stage 4A

The cancer has spread widely through the pleura or pericardium.

Stage 4B

The cancer has spread to other parts of the body through the blood or lymphatic system.

TNM staging

Thymoma and thymic carcinoma may also be staged using the TNM system.

Stage 1

The tumour is within the thymus or has grown into surrounding fat. The tumour may also have grown into the pleura that sits next to the thymus.

Stage 2

The tumour has grown into the pericardium.

Stage 3A

The tumour has grown into any of the following:

  • lungs
  • nearby large veins in the upper chest
  • large blood vessels going into or leaving the lung outside of the pericardium
  • nerve to the diaphragm (called the phrenic nerve)
  • chest wall

Stage 3B

The tumour has grown into any of the following:

  • the large artery leaving the heart (called the aorta)
  • an artery branching off the arch of the aorta
  • large blood vessels going into or leaving the lung within the pericardium
  • the muscle layer of the heart (called the myocardium)
  • windpipe (trachea)
  • esophagus

Stage 4A

The cancer has spread to lymph nodes around the thymus (perithymic lymph nodes) or the cancer has spread to a part of the pleura or pericardium that is not attached to the main tumour.

Stage 4B

The cancer has spread to lymph nodes deeper in the thorax (intrathoracic lymph nodes) or to lymph nodes in the neck (cervical lymph nodes).


The cancer has spread to other parts of the body (called distant metastasis), such as to the lungs, liver or bone.

Recurrent thymus cancer

Recurrent thymus cancer means that the cancer has come back after it has been treated. If it comes back in the same place that the cancer first started, it’s called local recurrence. If it comes back in tissues or lymph nodes close to where it first started, it’s called regional recurrence. It can also recur in another part of the body. This is called distant metastasis or distant recurrence.

Thymoma may come back up to 20 years after it is first treated. Thymic carcinoma most often comes back within 3 years after treatment.


The thin layer of tissue that covers the lungs and lines the chest cavity. It protects and cushions the lungs and produces a fluid that acts like a lubricant so the lungs can move smoothly in the chest cavity.

lymphatic system

The group of tissues and organs that produce and store cells that fight infection and diseases.

The lymphatic system includes the adenoids, tonsils, spleen, thymus, lymph nodes, lymph vessels and bone marrow.

Also called the lymph system.


The upper part of the body between the neck and abdomen that contains the respiratory system (the organs involved in breathing) and the heart.

Commonly called the chest.


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