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.

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.

Talk to your doctor if you have questions. Find out more about staging cancer.

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

The tumour is within the thymus or has grown into surrounding fat. The tumour may also have grown into the outside lining of the lung (the pleura) that sits next to the thymus.

The tumour has grown directly into the sac that surrounds the heart (the pericardium).

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

The cancer has spread to lymph nodes around the thymus.

OR

The cancer has spread to a part of the pleura or pericardium that is not attached to the main tumour (called drop metastases).

The cancer has spread to lymph nodes deeper in the chest or to the lymph nodes in the neck.

OR

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

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

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.

• T1a means the tumour is 5 cm or less in size.
• T1b means the tumour is larger than 5 cm.

The tumour has grown into the pericardium, the lung or the nerve that runs from the neck to the diaphragm (the phrenic nerve).

The tumour has grown into any of the following:

• the large veins in the upper chest going to the lungs
• the large arteries going into or away from the lungs
• the chest wall

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 away from the lungs within the pericardium
• the muscle layer of the heart (called the myocardium)
• windpipe (trachea)
• esophagus

The tumour can be at any stage, and it has spread directly to the:

• lymph nodes in the front part of the mediastinum
• lymph nodes in the deeper part of the chest
• pleura or the pericardium, but the area where the cancer cells are found isn't connected to the original tumour

The tumour can be at any stage and has spread directly to:

• lymph nodes deeper in the chest (intrathoracic lymph nodes) or to lymph nodes in the neck (cervical lymph nodes)
• the lungs
• the heart
• other parts of the body (called distant metastasis), such as to the lymph nodes outside of the chest, lungs, liver or bone

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.

Thymic carcinoma is more likely to recur than thymoma. It most often comes back within 3 years after finishing treatment.

Thymoma may come back up to 20 years after it is first treated. Thymoma tumours with a higher Masaoka stage (3 or 4) are more likely to come back than tumours with a lower stage (1 or 2).