Staging and grading of thymus cancer

The stage and grade of thymus cancer describes its size, whether it has spread and how quickly it may develop.

What is staging and grading?

After your tests to diagnose thymus cancer, doctors will use the results to find out more about the size and position of the cancer and whether it has spread. This is called staging.

A doctor will look at the cancer cells under a microscope to get an idea of how quickly the cancer might grow or spread. This is called grading.

Knowing the stage and grade of thymus cancer helps doctors decide the best treatment for you.

Staging of thymus cancer

The stage of a cancer describes its size and whether it has spread.

Staging of thymus cancer can be complicated. Your doctor or specialist nurse will explain more about the stage you have.

There are different ways of staging cancer. The TNM staging system or the number staging system are usually used for thymus cancer.

TNM staging system

The TNM system uses 3 important pieces of information:

  • T describes the size of the tumour. This is usually a number between 1 and 4. 1 is a small cancer. 4 is a larger or more advanced cancer.
  • N describes whether the cancer has spread to the lymph nodes. The number can be between 0 and 3. 0 means there are no cancer cells in the lymph nodes. 3 means more lymph nodes are affected by cancer.
  • M describes whether the cancer has spread to another part of the body. This is known as metastatic or secondary cancer. The number is either 0 or 1. 0 means the cancer has not spread to other parts of the body. 1 means it has spread.

Number staging system

  • Stage 1 means the cancer is only in the thymus and has not spread outside it.
  • Stage 2a means the cancer has started to spread into the outer layer of tissue of the thymus.
  • Stage 2b means the cancer has grown through the outer layer of the thymus and may have spread to nearby fatty tissue, but not into the lining of the lungs (pleura) or the lining of the heart (pericardium).
  • Stage 3 means the cancer has spread into nearby organs such as the lungs or lining of the heart (pericardium) and may have grown into blood vessels near the heart.
  • Stage 4A means the cancer has spread widely into the lining of the lungs (pleura) and the covering layer of the heart (pericardium) and has spread to lymph nodes nearby.
  • Stage 4B means the cancer has spread to other organs, such as the liver.

Type and grade of thymus cancer

The doctor examines the cancer cells under a microscope to find out the type and grade of thymus cancer you have. This gives them an idea of how the cancer may develop and how quickly it may grow. This can help your doctor to decide if you need more treatment after surgery.

The type describes the type of cell the cancer has started growing from. It also tells your doctor if the cancer is a thymoma or a thymic tumour.

The grade of the cancer describes how different the cancer cells look from normal cells.

Thymoma groupings

Doctors may group thymomas using the World Health Organisation (WHO) system. This uses letters from A to C, sometimes with numbers added, for the different types of thymoma. This is based on how the cells look under the microscope.

  • Type A is the rarest type of thymoma. The cells in the tumour look quite normal.
  • Type AB is also called a mixed thymoma. There are lymphocyte cells as well as thymus cells in the tumour.
  • Type B1 has a lot of lymphocytes, along with normal looking thymus cells.
  • Type B2 has a lot of lymphocytes and the thymus cells in the tumour look bigger than normal.
  • Type B3 has few lymphocytes and the thymus cells look abnormal.
  • Thymic cancer is previously known as Type C. The thymus cells look very abnormal.

The most common type of thymoma is AB. This type can often be treated successfully. Most type B thymomas can also be treated successfully. Thymic cancer is often more advanced when it is diagnosed, so it can be harder to treat.

About our information

  • References

    Below is a sample of the sources used in our thymus cancer information. If you would like more information about the sources we use, please contact us at

    ESMO Annals of Oncology. Thymic Epithelial Tumours: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up: 2015. Available from (accessed July 2021)

    Marx A, Chan JK, Coindre JM, et al. The 2015 World Health Organization Classification of Tumours of the Thymus: Continuity and Changes. Journal of Thoracic Oncology 2015; 10: 1383-95 (accessed July 2021)

    International Thymic Malignancy Interest Group (ITMIG): About Thymic Tumours - symptoms, staging, standard treatment options. Available from (accessed July 2021)

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr David Gilligan, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

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Date reviewed

Reviewed: 01 September 2022
Next review: 01 September 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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