Breast Cancer Stages - how are they determined and what do they mean?

Updated: Mar 17

Breast cancer staging is complicated. The American Joint Committee on Cancer (AJCC) has designated the TNM method (T = tumor size, N = lymph node involvement, M = metastasis) to stage breast cancer. Here I will try to simplify the breast cancer staging technique.

Breast cancer patient taking a mammogram.

What are the stages of breast cancer?

There are 4 stages (anatomic stage group) of breast cancer. They are stages I, II, III and IV. There are many sub-stages and they are defined with the letters A, B and C. The breast cancer stage is determined by the TNM score. To learn more about breast cancer treatment options and outcomes, please visit

The 'T' in the TNM method of breast cancer staging

In breast cancer staging using TNM method, the T represents the clinical and pathological stage of the tumor. There are several T categories. Here, I will discuss some of them.

T0 = no evidence of primary breast tumor

T1 = breast tumor is less than or equal to 20 mm (2 cm) in greatest dimension

T2 = breast tumor is greater than 20 mm (2 cm) but is less than equal to 50 mm (5 cm) in greatest dimension

T3 = breast tumor is greater than 50 mm (5 cm) in the greatest dimension

T4 = breast tumors with an extension into the chest wall or skin or both. There are many subcategories, which we will not discuss here

The 'N' in the TNM method of breast cancer staging

In breast cancer staging, the involvement of lymph nodes that are clinically significant is defined with cN. Based on the many different criteria, there are many categories and sub categories. Here, I will discuss only a few of them for the sake of simplicity. The term cN0 signifies no lymph node metastasis, cN1 signifies metastasis into the internal mammary lymph nodes and level I and II auxiliary lymph nodes, cN2 signifies metastasis into the internal nodes with out auxiliary level I and II metastasis or into the auxiliary nodes that are clinically and last but not the least, cN3 signifies further spread into the infraclavicular lymph nodes (level III auxiliary) and supraclavicular lymph nodes with or without metastasis into level I and II lymph nodes. There are many other subcategories, which I will not discuss here. Regional lymph nodes are also identified as pathological pN categories.

The 'M' in the TNM method of breast cancer staging

The distant metastasis is defined by M. Using clinical and radiographic means to detect metastasis, when no evidence of distant metastasis is found it is called M0. Whereas, cM1 signifies detection of metastasis through clinical and radiographic means and pM1 signifies histologically proven metastasis in distant organs.

Now let us learn about the anatomical staging

Stage IA T1, No, M0 Tumor < 2 cm, no lymph node, no distant metastasis

Stage IB T0/T1, N1mi, M0 Tumor <2 cm, micro-metastasis in lymph nodes (~ 200

cells), no distant metastasis

Stage IIA T1, N1, M0 No distant metastasis, tumor size < 5 cm, internal

T2, No, Mo mammary lymph node metastasis

T0, N1, M0

Stage IIB T2, N1, M0 No distant metastasis, tumor size > 5 cm, internal

T3, N0, M0 mammary lymph node metastasis

Stage IIIA T0, N2, M0 No distant metastasis, any tumor size, lymph nodes

T1, N2, M0 outside breast tissues have cancer cells

T2, N2, M0

T3, N1, M0

T3, N2, M0

Stage IIIB T4, N0, M0 No distant metastasis, tumor extended into the chest

T4, N1, M0 wall or skin, internal mammary lymph nodes involved

Stage IV Any T, any N, M1 Distant metastasis present (in other body parts) and

could have any size of tumor and any type of lymph

node involvement.

#breastcancer #cancer #breastcancerstaging



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Author: Anirban Mukherjee, PhD

Founder, Cancer Therapies 4 U LLC

Research Scientist at the University of Texas at Austin

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