Understand Breast Cancer Staging: TNM Classification of Breast Cancer


Staging helps to determine the disease prognosis and to select an appropriate treatment strategy.

We us TNM most commonly used system for breast cancer staging. It uses mainly 3 parameters: “T” stands for “Tumor”; “N” for “Lymph Nodes”; and “M” for “Metastasis”.

Numbers and/or letters after T (0, is, 1, 2, 3, and 4), N (0, 1mi, 1, 2, and 3), and M (0 and 1) provide more details about each of these parameters. Once T, N, and M are determined, it is used to assign an overall stage (from 0 to IV).

Breast Cancer Staging explained:

Tis – Pre-cancerous changes or carcinoma in situ (CIS). No spread to nearby lymph nodes or distant body parts.

T1 – Tumor size is 2 cm or less. No spread to nearby lymph nodes or distant body parts.

T2 – Tumor size >2 cm, but </=5 cm. No spread to nearby lymph nodes or distant body parts.

T3 – Tumor size >5 cm. No spread to nearby lymph nodes or distant body parts.

T4 – Tumor of any size with direct extension to the chest wall or skin or inflammatory breast cancer. 

T Staging

N1 – Cancer spread to 1-3 axillary lymph nodes or tiny cancer deposits in internal mammary lymph node(s) on sentinel lymph node biopsy.

N2 – Cancer spread to 4-9 axillary lymph nodes or enlargement of internal mammary lymph node(s). 

N3 – >/=10 axillary lymph nodes (>/=1 area >2 mm), or cancer spread to the infraclavicular (those under the collarbone) lymph nodes (>/=1 area >2 mm) [N3a],

Cancer spread to >/=1 axillary lymph nodes (>/=1 area >2 mm) with internal mammary lymph node(s) enlargement, or cancer spread to >/=4 axillary lymph nodes (>/=1 area >2 mm) with micrometastasis in internal mammary lymph node(s)[N3b], or

cancer spread to the supraclavicular (those above the collarbone) lymph nodes (>/=1 area >2 mm)[N3c].

N Staging

M1 – Cancer spread to distant organs like bones, lungs, liver, brain, etc.

M Staging
0Tis N0 M0
IAT1 N0 M0
IBT0-1 N1mi M0
IIAT0-1 N1 M0
T2 N0 M0
T3 N0 M0
IIIAT0-2 N2 M0
T3 N1-2 M0
IIIBT4 N0-2 M0
IVAnyT AnyN M1

In addition to staging, estrogen receptor (ER), progesterone receptor (PR), HER2/neu (HER2) status, and grade of the cancer is evaluated on the surgical specimen to assess the prognosis of the disease, and planning the treatment.

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Watch the video below to better understand the anatomy and staging of breast cancer and axillary lymph nodes:


Video Transcript:

The staging of breast cancer is called TNM staging. We will discuss this in detail.

It is called as T1 when the tumor size is less than or equal to 2 cm.

T2 when the tumor is 2 cm to 5 cm.

And T3 when the tumor is more than 5 cm.

To understand T4 disease, first we have to know the structures. Deep to the breast there is pectoralls fascia and pectoralls major muscle.

And here lies the pectoralis minor muscle.

Other structures in the chest wall include ribs and intercostal muscles.

If we look from the front of the chest, this is the pectoralis major muscle.

And this is the serratus anterior muscle.

T4a disease is when the tumor infiltrates the chest wall, not including only pectoralis muscle adhesion or invasion.

And here, the tumor infiltrates into the serratus anterior muscle.

T4b disease is involvement of skin by the tumor.

It can present as skin ulceration or as satellite tumor nodules.

Or as edema of skin looking like an orange peel known as peau de orange.

All the skin changes should occupy less than one-third of the surface area of breast to be called as T4b. Infiltration of tumor into both, chest wall and skin, i.e., T4a and T4b both, is called T4c.

And when the breast cancer progresses very rapidly to cause diffuse erythema and edema of skin breast, involving more than one-third of the skin, then it is called as inflammatory breast cancer.

Now, we move on to the N-staging. To understand the N staging, first you have to know the local structures in that area.

In this figure, you can see the humerus, clavicle and sternum bone.

This is the pectoralls minor muscle.

These nodular structures in the anterior axillary fold, are called as anterior group of lymph nodes.

And along the head of the humerus are lateral group of lymph nodes.

All these three groups, lateral to pectoralis minor muscle, are level 1 lymph nodes.

These present behind the pectoralls minor muscle are central, or level 2 lymph nodes.

And these present medial to pectoralls minor muscle, are apical or level 3 lymph nodes.

And these, along the sternum are called as internal mammary lymph nodes.

For clinical N-staging, we have to palpate level 1 and 2 lymph nodes in axilla. If they are not palpable, it is NO. If palpable, and freely mobile, it is N1. If level 1 or level 2 lymph nodes are palpable, but they are fixed or matted, it is called as N2a.

If only internal mammary lymph nodes are seen in CT scan without any level 1 or level 2 nodes, the it is called as N2b.

If infraclavicular lymph nodes are involved, it is called as N3a.

If internal mammary and axillary lymph nodes both are involved that is N2a and N2b, then it is N3b.

Involvement of supraclavicular lymph nodes are called as N3c.

Now, let’s move ahead. Next comes the M-staging, if the disease has spread to the distance organ it is called as M1 otherwise it is M0. This figure shows spread to both lungs in the form or multiple metastatic nodules.

And here, metastasis to the pleura has resulted in fluid collection, called as pleural effusion.

This figure shows spread to the liver in form or multiple nodular deposits.

And here, the cancer is spread to the adrenal gland.

Similarly, the spread may occur to brain, bones or other part of the body.

After we have staged the disease, we broadly divide the breast cancer into a particular stage group, ie, whether it is a localised, locally advanced or metastatic breast cancer, as shown in the infographic below.

Watch the video below to better understand the STAGE GROUPING of breast cancer.

Video Transcript:

To make things easier, we stage the breast cancer into stage groups. It can broadly be divided into localized, locally advanced or metastatic disease.

Localised disease includes cases up to T2 N1 M0 and T3 N0 M0. Starting from T3 N1 M0 and onwards all N2 and N3 and T4 cases are included under locally advanced disease. Metastasis to other sites, as we have discussed previously is called M1 disease.

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