The American Joint Committee on Cancer (AJCC) and the International Union for Cancer Control (UICC) maintain the TNM classification system as a tool to describe the extent of the cancer in the body. It is based on whether the cancer is invasive or non-invasive, the size of the tumor, how many lymph nodes are involved, and if it has spread to other parts of the body. It’s updated every 6 to 8 years to include advances in our understanding of cancer.

Staging Breast Cancer

To further define our patient population, all patients with a diagnosis of breast cancer are staged according to the TNM system.

The stage of a breast cancer can be based either on the results of physical exam, biopsy, and imaging tests (called the clinical stage), or on the results of these tests plus the results of surgery (called the pathologic stage). The staging described here is the pathologic stage, which includes the findings after surgery, when the pathologist has examined at the breast mass and nearby lymph nodes. Pathologic staging is likely to be more accurate than clinical staging, as it allows the doctor to get a firsthand impression of the extent of the cancer.

The TNM staging system classifies cancers based on their T, N, and M stages:

  • The letter T followed by a number from 0 to 4 describes the tumor’s size and spread to the skin or to the chest wall under the breast. Higher T numbers mean a larger tumor and/or wider spread to tissues near the breast.
  • The letter N followed by a number from 0 to 3 indicates whether the cancer has spread to lymph nodes near the breast and, if so, how many lymph nodes are affected.
  • The letter M followed by a 0 or 1 indicates whether the cancer has spread to distant organs — for example, the lungs or bones.

Primary tumour (T)

TX Primary tumour cannot be assessed
T0 No evidence of primary tumour
Tis Carcinoma in situ
T1 Tumour ≤ 20 mm in greatest dimension
T1mi Tumour ≤ 1 mm in greatest dimension
T1a Tumour > 1 mm but ≤ 5 mm in greatest dimension
T1b Tumour > 5 mm but ≤ 10 mm in greatest dimension
T1c Tumour > 10 mm but ≤ 20 mm in greatest dimension
T2 Tumour > 20 mm but ≤ 50 mm in greatest dimension
T3 Tumour > 50 mm in greatest dimension
T4 Tumour of any size with direct extension to the chest wall and/or to the skin (ulceration or skin nodules)
T4a Extension to chest wall, not including only pectoralis muscle adherence/invasion
T4b Ulceration and/or ipsilateral satellite nodules and/or oedema (including peau d’orange) of the skin
T4c Both T4a and T4b
T4d Inflammatory carcinoma

Axillary Lymph Nodes (N)*

N0(i-) No regional lymph node metastases histologically.
N0(i+) Malignant cells in regional lymph node(s) ≤ 0.2 mm
N1 Micrometastases; or metastases in 1-3 axillary lymph nodes and/or in internal mammary nodes, with metastases detected by sentinel lymph node biopsy
N1mi Micrometastases (> 0.2 mm and/or > 200 cells, but none > 2.0 mm)
N1a Metastases in 1-3 axillary lymph nodes (at least 1 metastasis > 2.0 mm)
N1b Metastases in internal mammary nodes, with micrometastases or macrometastases detected by sentinel lymph node biopsy
N1c Metastases in 1-3 axillary lymph nodes and in internal mammary lymph nodes, with micrometastases or macrometastases detected by sentinel lymph node biopsy
N2a Metastases in 4-9 axillary lymph nodes (at least 1 tumour deposit > 2.0 mm)
N2b Metastases in clinically detected‡ internal mammary lymph nodes in the absence of axillary lymph node metastases
N3a Metastases in ≥ 10 axillary lymph nodes (at least 1 tumour deposit > 2.0 mm); or metastases to the infraclavicular (level III axillary lymph) nodes
N3b Metastases in clinically detected‡ ipsilateral internal mammary lymph nodes in the presence of ≥ 1 positive axillary lymph nodes; or in > 3 axillary lymph nodes and in internal mammary lymph nodes, with micrometastases or macrometastases detected by sentinel lymph node biopsy
N3c Metastases in ipsilateral supraclavicular lymph nodes

Distant metastasis (M)

M0 No clinical or radiographic evidence of distant metastasis
M1 Distant detectable metastases present

Once the T, N, and M categories have been determined, this information is combined in a process called stage grouping. Cancers with similar stages tend to have a similar outlook and are often treated in a similar way. Stage is expressed in Roman numerals from stage I (the least advanced stage) to stage IV (the most advanced stage). Non-invasive cancer is listed as stage 0.



Primary tumour (T)
Stage T N M
0 Tis N0 M0
IA T1 N0 M0
IB T0 N1mi M0
T1 N1mi M0
IIA T0 N1 M0
T1 N1 M0
T2 N0 M0
IIB T2 N1 M0
T3 N0 M0
IIIA T0 N2 M0
T1 N2 M0
T2 N2 M0
T3 N1 M0
T3 N2 M0
IIIB T4 N0 M0

By staging each case according to the information provided by our Anatomical Pathologists who examined the removed tissue we are able to accurately allocate a patient to the correct stage grouping. It is now possible to look at survival by the described grouping.

Where to now?

Research into the causes, prevention, and treatment of breast cancer is being done in many medical centers throughout the world. The Strathfield Breast Centre is part of that network and is continually looking to advance knowledge using the information contained in our database, and by collaboration with other Centre’s of excellence.

If you have a question, e-mail us at: info@tsbc.com.au