TNM Classification of Oral Cancer

The TNM Classification is a method used to stage cancers. It is used for all cancers of the body, but for this post, we will be focussing on the TNM Classification for oral cavity cancers.

What is the TNM Classification?

The TNM Classification is used to stage a tumour. Staging is different from grading, as grading describes how similar the cells of a tumour are to ‘healthy’ cells, whilst staging describes how advanced a cancer is. The TNM classification is divided in to:

• T – Tumour – this looks at the size of the tumour as well as the depth of invasion of the tumour i.e. how deep the tumour has infiltrated
• N – Nodes – this looks at the number of lymph nodes involved locally, the size of lymph nodes, the location of the lymph nodes and if there is any extranodal extension (ENE). Extranodal extension, previously referred to as extracapsular spread, describes a when a cancer has spread out of a lymph node and started affecting surrounding tissues
• M – Metastasis – this looks at whether the cancer has spread distant to the primary site, to other parts of the body

In this post, we will be looking at the TNM-8 classification, which was developed in 2018. There are some key differences between the TNM-8 system, and the previous TNM-7 system:

• Depth of invasion – TNM-8 addresses the depth of invasion, which TNM-7 does not
• Extranodal extension – TNM-8 addresses extranodal extension, which TNM-7 does not

These differences are due to updated knowledge identifying these factors are key prognostic factors which impact patient outcomes. However, currently both the TNM-8 and TNM-7 systems are used simultaneously.

Tumour

Tx

This describes a tumour that cannot be assessed

Tis

This describes a tumour which is limited to a single layer of tissue, also referred to as carcinoma in situ.

T1

This describes a tumour which is 2cm or less in its greatest dimension. Additionally, the depth of invasion of the tumour is 5mm or less.

T2

This is where a tumour is 2cm or small and the depth of invasion is between 5 and 10mm. Or, alternatively, the tumour is greater than 2cm but not 4cm and the depth of invasion is 10mm or less.

T3

This is where a tumour is larger than 4cm or any tumour with a depth of invasion greater than 10mm.

T4

This is a moderately advanced or very advanced local disease. It is divided in to T4a, where the tumour has invaded nearby structures in the mouth such as the bone or sinuses. There is also T4b, which is when the tumour has invaded the muscles or the base of the skulls and/or encasing internal arteries.

Nodes

Nodes can be assessed in two ways – clinical or pathological. Clinical is based on physically assessment of the patient. Pathological is once surgery has been carried out and the lymph nodes have been assessed under a microscope. We will look at the pathological staging below.

Nx

This is where the lymph nodes cannot be assessed.

N0

There is no evidence of cancer in the regional lymph nodes.

N1

This is where cancer has spread to a single lymph node on the same side, or ipsilateral side, as the primary tumour. The nodes is 3cm or smaller in size and there is no ENE.

N2a

This is where cancer has spread to a single lymph node and is 3cm or smaller, but there is ENE. Alternatively, the cancer has spread to a single lymph node on the same side as the tumour and is larger than 3cm but not 6cm, and there is no ENE.

N2b

This is when the cancer has spread to more than 1 lymph node on the same side as the primary tumour, but none measure larger than 6cm. There is also no ENE.

N2c

This is when the cancer has spread to more than 1 lymph node on either side of the body and none measures larger than 6cm. There is no ENE.

N3a

This is when the cancer is found in a lymph node and is larger than 6cm. There is no ENE.

N3b

This is where there is ENE in a single lymph node on the same side as the tumour, and it is larger than 3cm. Or, the cancer has spread to many lymph nodes, and at least one has ENE. Alternatively, there is ENE in a single lymph node on the opposite side of the primary tumour and it is 3cm or smaller.

Metastasis

This is simply divided in to M0, where there is no spread to other parts of the body, or M1, where there is spread to other parts of the body.

Conclusion

• The TNM classification is a method of staging cancers
• Tumour looks at the size and depth of invasion of the tumour
• Nodes address the number, size, location and extranodal extension of regional lymph nodes
• Metastasis looks at distant spread of the cancer

Useful Links & Recommended Reading

• Oral Cancer Grading and Staging
• Single Best Answer Questions for Dentistry