What is staging? 

Once your doctor has made a diagnosis of cancer, it is important that they assess the extent (or stage) of the cancer. Staging a cancer is important because it helps doctors to choose the best treatment for you. It also gives information about the chances of cure. The stage is based on the size of the cancer, whether it has invaded into nearby areas and whether it has spread to lymph nodes in the neck (called lymph node metastases) or other sites in the body, such as the lungs, liver or bone (called distant metastases).

The TNM (Tumour, Node, Metastases) system is used to stage cancer. This system is used to summarise information about the size of the cancer and whether it has spread to lymph nodes or other parts of the body.

The TNM system
T T stands for the size of the cancer. A T value can range from 1 (small and localised to the thyroid) to 4 (invading into other structures).
N N indicates whether the cancer has spread to the lymph nodes. Where there is no cancer in the lymph nodes, the N value is 0. An N value can range from 1 to 3, depending on the size and number of cancerous lymph nodes.
M M stands for distant metastases, or whether the cancer has spread to other parts of the body outside the head and neck. An M value can be either 0 (cancer has not spread to other parts of the body) or 1 (cancer has spread to other parts of the body).

Once the values for T, N and M have been worked out, they are combined to give an overall score between 1 and 4. Your doctor may write these as Roman numerals: I, II, III and IV. 

Thyroid cancer is very different to other head and neck cancers, because the stage depends on your age. Staging is complicated but in broad terms the higher the stage, the greater the extent, spread or invasion of the thyroid cancer.

It is important to realise that the staging systems for thyroid cancers are very different to other cancers and sometimes not very accurate in predicting the chances of cure for an individual. This is because a high number of people with stage III and IV well-differentiated thyroid cancer (papillary and follicular) are cured with appropriate treatment. It is important you discuss the stage of your cancer with your doctors to understand what it means for you.

What is grading? 

Staging and grading are not the same. Your doctor may also be interested in the grade of the cancer. Grading refers to the growth pattern of the cancer. The grade of the cancer is determined by a pathologist who examines the biopsy sample under a microscope. The pathologist determines the grade of the cancer by how the cells look. The grade can be used to estimate how quickly the cancer is likely to grow and spread.  For thyroid cancers, grading is usually described as either well differentiated (papillary and follicular) which have a good prognosis or poorly differentiated (including anaplastic and de-differentiated) which often have a poor prognosis.