TNM Staging System for Breast Cancer

After a woman is diagnosed with breast cancer, doctors will try to find out if it has spread, and if it has, then how far. This process is called the Staging of Cancer.

The stage of cancer tells how much cancer has spread in the body. It helps to determine how serious the cancer is and what is the best treatment for cancer. Doctors also tell by cancer’s stage about the approximate survival statistics.

`breast cancer stages

The breast cancer TNM staging system is the common way used by the doctors to stage breast cancer, more precisely. TNM stands for Tumor, Node, and Metastasis. The scans and tests of the patient can give some information about the stage of your cancer.

But the doctor might not be able to tell the exact stage until the patient has surgery. 

The earliest stage of Breast Cancer is stage 0, also known as “Carcinoma in situ”. The Cancer then ranges from stage I ( one ) to stage IV ( four ). The lower the number of the stage is, the less cancer has spread in the female. A higher number, such as stage IV indicates that cancer has spread more across the body. And in a particular stage, an earlier letter means that the stage is lower.

Breast Cancer Stage grouping

Doctors use the TNM system to assign an overall stage to cancer from 0 to 4 for various types of cancer. Stages 1 to 4 are usually named as the Roman numerals I, II, III, and IV but numerics can also be used. Generally, the higher the number is, the more cancer has spread and thus more severe is the condition. Sometimes, the stages are subdivided into more detailed categories, using the letters A, B or C. The stages of Cancer and what they mean is briefed below:

breast cancer stage 0 and 1

  • Stage 0 – Carcinoma in situ, the pre-cancerous change.

  • Stage 1 – The tumor is usually very small, in the initial stage and hasn’t grown outside that organ where it originated.

stage 2 of breast cancer

  • Stages 2 – The tumor has grown outside the organ where it originated, into nearby tissue.stage 3 of breast cancer
  • Stage 3- The Cancer has spread to nearby lymph nodes, chest wall or even the skin of the breasts.stage 4 of breast cancer
  • Stage 4 – The cancer has grown aggressively and spread through the blood or lymphatic system to distant organs in the body. This is known as the metastatic spread.

Also Read: Fibrocystic Breast Disease

How is the stage of Cancer determined?

The staging system most often used for breast cancer is the TNM system, which is based on 7 key factors:


  • The extent or size of the tumor (T): The doctor needs to know that large is cancer and if it has grown into the nearby areas or not.
  • The spreading to nearby lymph nodes (N): The doctor needs to know if cancer spread to nearby lymph nodes or not. If the cancer has spread to the nearby lymph nodes, then it has to be evaluated on how many lymph nodes cancer has spread.
  • The spread to distant sites (M- Metastasis): The doctor needs to know if cancer has cancer spread to distant organs like the lungs or liver or not.


  • Status of Estrogen Receptor (ER): It has to be evaluated if cancer has the protein called an estrogen receptor or not.
  • Progesterone Receptor (PR) status: The doctor needs to know if cancer has the protein known as ‘progesterone receptor’.
  • Her2/neu (Her2) Status: The doctor has to know if cancer makes too much of the protein called ‘Her2’ or not.
  • Grade or Stage of cancer (G): The doctor needs to know much do the cancer cells look like normal cells.

The system of TNM has both clinical and pathologic staging systems for various breast cancers.

The pathologic stage, also known as the surgical stage,  is discovered by examining the tissues removed during the operation. In case, the surgery is not possible for the patient, the patient is suggested to undergo a clinical-stage instead. This is based on the results of the physical exam, followed by a biopsy, and imaging tests. The clinical-stage is helpful to plan the treatment ahead. 

Numbers or letters after T, N, and M give more details on each of the factors mentioned above. Higher numbers indicate that the cancer is in a more advanced stage. Once the female’s T, N, and M categories and ER, PR, Her2 status and grade of cancer have been determined, all the three are combined by the process called stage grouping to assign an overall stage of the patient.

Breast Cancer is a complex disease and needs a thorough evaluation. Detailed explanations of the TNM categories are mentioned below. The details about the ER, PR, and Her2 status and the grade of cancer have made the stage grouping complex, but it is very helpful and essential to know about the right stage and condition of the patient.

Brief of the TNM Staging System

TNM Staging System of Breast Cancer

T categories of Breast Cancer

T followed by a number ranging from 0 to 4 which describes the primary tumor’s size. It also indicates if the cancer has spread to the skin or the chest wall ( present under the breast ) of the patient.

Higher T numbers indicate a larger tumor which may have a wider spread to the nearby tissues around the breast.

  • TX: This indicates that the primary tumor cannot be assessed.
  • T0: This indicates that there is no evidence of primary tumor.
  • Tis: This indicates Carcinoma in situ (DCIS, or Paget disease of the nipple and has no associated tumor mass present)
  • TI (includes TIa, TIb, and TIc): This indicates the size of the tumor if the tumor is 2 cm (3/4 of an inch) or less across.
  • T II : This indicates that the tumor is more than 2 cm but not more than 5 cm (2 inches) across.
  • T III : This indicates that the tumor is more than 5 cm across.
  • T IV : (includes T4a, T4b, T4c, and T4d): This verifies if there is a tumor of any size present or growing into the chest wall or skin. This also includes Inflammatory Breast Cancer.

N categories for Breast Cancer

In the N category, N is followed by a number from 0 to 3, stating the spread of the disease. It tells if the cancer has spread to nearby lymph nodes or not. And, if it has spread, then how many lymph nodes are affected by cancer.

Lymph node staging for breast cancer is based on how the lymph nodes appear under the microscope. With advancement and change, technology has brought many improvements and the microscopic view can help the doctor determine the spread of cancer.

Advanced methods have made it possible to find even the smallest collections of cancer cells in the body.

It is not clear yet how much cancer needs to be present in the lymph node in order to see a change in outlook or treatment. This factor is still being studied. But, for now, a deposit of cancer cells must contain at least 200 cells or has been at least 0.2 mm across to change the N stage.

An area of cancer spread which is less than 0.2 mm or less than 200 cells, does not change the stage but is marked with certain abbreviations (i+ or mol+) which indicates the type of special test to find the spread of cancer.

consultation for breast cancer

If the area to which cancer has spread is at least 0.2 mm or 200 cells in number, but still not larger than 2 mm (one mm is approximately the size of a grain of rice), it is termed as micrometastasis. If the areas of cancer spread are larger than 2 mm, they can affect the outlook and change the overall N stage. The larger areas are sometimes at times macrometastases, but in most cases, it is just metastases.

  • NX: The nearby lymph nodes cannot be evaluated. It cannot be detected if the lymph nodes have been removed previously.
  • N0: This indicates that the cancer has not spread to any nearby lymph nodes.
  • N0(i+): The spread of cancer is up to less than 200 cells and is smaller than 0.2 mm. The “i+” means that a small number of cancer cells known as the isolated tumor cells were detected during routine stains or when immunohistochemistry, a special type of staining technique is used.
  • N0(mol+): Cancer cells cannot be detected in underarm lymph nodes, even while using special stains, but traces of cancer cells can be seen using a technique known as RT-PCR. This technique is a molecular test which can detect even very small numbers of cancer cells. This test is not used often to detect breast cancer cells in lymph nodes as the result does not influence the treatment decisions.


  • N1: Cancer has spread to 1 to 3 axillary nodes, found in the armpits or small amounts of cancer is found in the internal mammary lymph nodes, found near the breast bone, with sentinel lymph node biopsy.
  • N1mi: This indicates Micrometastases, which means that tiny areas of cancer spread in the lymph nodes under the arm. The areas where the cancer has spread in the lymph nodes are about 0.2mm across but are not larger than 2mm.
  • N1a: This indicates that cancer has spread to 1 – 3 lymph nodes under the arm with at least one area of cancer spread which is more than 2 mm across.
  • N1b: This indicates that the cancer has spread to internal mammary lymph nodes. But this spread can only be found with the ‘sentinel lymph node biopsy’ It does not cause the lymph nodes to get enlarged.
  • N1c: Both N1a and N1b apply in this case.


  • N2: This indicates that the cancer has spread to 4 to 9 lymph nodes under the arm, or the cancer has enlarged the internal mammary lymph nodes.
  • N2a: This indicates that the cancer has spread to 4 to 9 lymph nodes under the arm. The area of spread of cancer is larger than 2 mm.
  • N2b: This indicates that the cancer has spread to one or more internal mammary lymph nodes, which has made them enlarged

N3: Any of the following below:

  • N3a: It is either:

The Cancer has spread till 10 or more axillary lymph nodes, and has at least one area of cancer spread more than 2 mm, Or , The spread of the cancer is up to the lymph nodes under the collarbone, also called the infraclavicular nodes, with at least one area of cancer spread more than 2 mm.

  • N3b: It is either:

The cancer is detected in at least one axillary lymph node with at least one area of cancer spread more than 2 mm and has caused the internal mammary lymph nodes to enlarge, Or , The cancer has spread up to 4 or more axillary lymph nodes with at least one area of cancer spread more than 2 mm. Small amounts of cancer are found in the internal mammary lymph nodes with the sentinel lymph node biopsy.

  • N3c: This indicates that the cancer has spread till the supraclavicular nodes, the lymph nodes above the collarbone, with at least one area of cancer spread more than 2 mm.

M categories for Breast Cancer

Metastatic Breast Cancer

The image above shows the impact of Metastatic Cancer on the body 

  • M is followed by the numbers 0 or 1 which tells whether the cancer has spread to other distant organs such as, lungs, liver, or bones.
  • MX: Distant spread of cancer, ( the metastasis phase ), cannot be assessed.
  • M0: No distant spread can be detected on x-rays, other imaging tests or by physical examination.
  • cM0(i+): Small numbers of cancer cells are seen in the blood or bone marrow. This can only be found by special tests. There is are small areas of cancer spread which are no larger than 0.2 mm. These are found in the lymph nodes far from the underarm, collarbone, or the internal mammary areas.
  • M1: Cancer has spread to the distant organs, most often to the bones, lungs, brain, or liver.



The above mentioned TNM System is also briefed in the tables mentioned below.  

“T”  -Tumor“N”  -Lymph Nodes“M”  -Metastatic 

T 0- No tumor present.

Tis- Tumor has not spread to nearby tissues.

T I to T IV – Tumor has spread to nearby tissues

N 0- No cancer found in the lymph nodes.

NI to N III – Cancer has grown to lymph nodes.

M 0- Cancer has not spread to other parts of the patient’s body.M I- cancer has spread to other parts.


Using the T, N, and M values, the table below can help find the stage of the Cancer. Make sure you also consult your doctor as the condition may vary from patient to patient. 

Overall Stage                          T                                              M                    
Stage 0TisN 0M 0
Stage 1T 1N 0M 0
Stage II AT 0

T 1

T 2

N 1



M 0
Stage II BT 2

T 3

N 1

N 0

M 0
Stage III AT 0

T 1

T 2

T 3

T 3

N 2

N 2

N 2

N 1

N 2

M 0
Stage III BT 4Any NM 0
Stage III CAny TN 3M 0
Stage IV Any TAny NM 0


The TNM staging system links the important tumor characteristics with the survival data to help make an estimate and follow up with the outcomes. It shows clinical evaluation methods and treatments. The individual patient’s clinical course and the outcome cannot be predicted with any assurance. The available survival data, researches and staging system can only help formulate treatment decisions and provide an estimate of the likely prognosis.

Also Read: Breast cancer types

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