2002 American Joint Committee on Cancer (AJCC) TNM Staging System for the Breast

Tx: Primary tumor cannot be assessed
T0: No evidence of primary tumor
Tis: Carcinoma in situ
T1: Tumor 2 cm or less in greatest dimension
  T1mic Microinvasion 0.1 cm or less in greatest dimension
  T1a Tumor more than 0.1 cm but not more than 0.5 cm in greatest dimension
  T1b Tumor more than 0.5 cm but not more than 1 cm in greatest dimension
  T1c Tumor more than 1 cm but not more than 2 cm in greatest dimension
T2: Tumor more than 2 cm but not more than 5 cm in greatest dimension
T3: Tumor more than 5 cm in greatest dimension
T4; Tumor of any size with direct extension to (a) chest wall or (b) skin, only as described below
  T4a Extension to chest wall, not including pectoralis muscle
  T4b: Edema (including peau d'orange) or ulceration of the skin of the breast or satellite skin nodules confined to the same breast
  T4c Both T4a and T4b
  T4d Inflammatory carcinoma

Nx: Regional lymph nodes cannot be assessed (e.g., previously removed, or not removed for pathologic study)
N0: No regional lymph node metastasis histologically, no additional examination for isolated tumor cells (ITC)

Note: Isolated tumor cells (ITC) are defined as single tumor cells or small cell clusters not greater than 0.2 mm, usually detected only by immonohistochemical (IHC) or molecular methods but which may be verified on H&E stains. ITCs do not usually show evidence of malignant activity e.g., proliferation or stromal reaction.

pN0(i-) No regional lymph node metastasis histologically, negative IHC
pN0(i+) No regional lymph node metastasis histologically, positive IHC, no IHC cluster greater than 0.2 mm
pN0(mol-) No regional lymph node metastasis histologically, negative molecular findings (RT-PCR)
pN0(mol+) No regional lymph node metastasis histologically, positive molecular findings (RT-PCR)

Classification is based on axillary lymph node dissection with or without sentinel lymph node dissection. Classification based solely on sentinel lymph node dissection without subsequent axillary node dissection is designated (sn) for “sentinel node,” e.g., pN0(i+) (sn). RT-PCR: reverse transcriptase/polymerase chain reaction.

N1: Metastasis in 1 to 3 axillary lymph nodes, and/or in internal mammary nodes with microscopic disease detected by sentinel lymph node dissection but not clincially apparent
  N1mi: Micrometastasis (greater than 0.2 mm, none greater than 2.0 mm)
  N1a: Metastasis in 1 to 3 axillary lymph nodes
  N1b: Metastasis in internal mammary nodes with microscopic disease detected by sentinel lymph node dissection but not clinically apparent
  N1c: Metastasis in 1 to 3 axillary lymph nodes and in internal mammary nodes with microscopic disease detected by sentinel lymph node dissection but not .clnically apparent. (If associated with greater than 3 positive axillary lymph nodes, the internal mammary nodes are classified as pN3b to reflect increased tumor burden)
N2: Metastasis in 4 to 9 axillary lymph nodes, or in clinically apparent internal mammary lymph nodes in the absecne of axillary lymph node metastasis
  N2a: Metastasis in 4 to 9 axillary lymph nodes (at least one tumor deposit greater than 2.0 mm)
  N2b: Metastasis in clinically apparent internal mammary lymph nodes in the of axillary lymph node metastasis
N3: Metastasis in 10 or more axillary lymph nodes, or in infraclavicular lymph nodes, or in clinicllay apparent ipsilateral internal mammary lymph nodes in the of 1 or more positive axillary lymph nodes; or in more than axillary lymph nodes with clinically negative microscopic metastasis in internal mammary lymph nodes; or in ipsilateral supraclavicular lymph nodes
  N3a: Metastasis in 10 or more axillary lymph nodes (at least one tumor deposit greater than 2.0 mm), or metastasis to the infraclavicular lymph nodes
  N3b: Metastasis in clinically apparent ipsilateral internal mammary lymph nodes in the of 1 or more positive axillary lymph nodes; or in more than 3 axillary lymph nodes and in internal mammary lymph nodes with microscopic disease detected by sentinel lymph node dissection but not clinically apparent
  N3c: Metastasis in ipsilateral supraclavicular lymph nodes

Stage 0: Tis N0 M0
Stage I: T1* N0 M0
Stage IIA: T0 N1 M0, T1* N1 M0, T2 N0 M0
Stage IIB: T2 N1 M0, T3 N0 M0
Stage IIIA: T0 N2 M0, T1* N2 M0, T2 N2 M0, T3 N1 M0, T3 N2 M0

* T1 includes T1mic

Stage IIIB: T4 N0 M0, T4 N1 M0, T4 N2 M0
Stage IIIC: Any T N3 M0
Stage IV: Any T Any N M1