| Tx | Primary tumor cannot be assessed |
| T0 | No evidence of primary tumor |
| Tis | Carcinoma in situ |
| Tis (DCIS) | Ductal carcinoma in situ |
| Tis (LCIS) | Lobular carcinoma in situ |
| Tis Paget’s disease | Paget’s disease of the nipple with no tumor |
| T1 | Tumors < cm in greatest dimension |
| T1mic | Microinvasion < 0.1 cm in greatest dimension |
| T1a | Tumor > 0.5 cm but not more than 1 cm in greatest dimension |
| T1c | Tumor > 1 cm and not more than 2 cm in greatest dimension |
| T2 | Tumor > 2 cm and not more than 5 cm in greatest dimension |
| T3 | Tumor > 5 cm in greatest dimension |
| T4 | Tumor of any size with direct extension to (a) chest wall or (b) 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 TT4a and TT4ba |
| T4d | Inflammatory carcinoma |
| REGIONAL LYMPH NODES (N) | |
| Nx | Regional lymph nodes cannot be assessed (e.g., previously removed) |
| N0 | No regional lymph node metastasis |
| N1 | Metastasis to movable axillary lymph node(s) |
| N2 | Metastasis in ipsilateral axillary lymph nodes fixed or matted, or clinically apparent ipsilateral internal mammary nodes in the absence of clinically evident axillary lymph node metastasis |
| N2a | Metastasis to ipsilateral axillary lymph nodes fixed to one another (matted) or to other structures |
| N2b | Metastasis only in clinically apparent ipsilateral internal mammary nodes and in the absence of clinically evident axillary lymph node metastasis |
| N3 | Metastasis in ipsilateral infraclavicular lymph node(s) or clinically apparent ipsilateral internal mammary node(s) and in the presence of clinically evident axillary lymph node metastasis; or metastasis in ipsilateral supraclavicular lymph node(s) with or without axillary or internal mammary lymph node involvement |
| N3a | Metastasis in ipsilateral infraclavicular lymph node(s) and axillary lymph node(s) |
| N3b | Metastasis in ipsilateral internal mammary node(s) and axillary lymph nodes(s) |
| N3c | Metastasis in ipsilateral supraclavicular lymph node(s) |
| PATHOLOGICAL CLASSIFICATION (PN) | |
| pNx | Regional lymph nodes cannot be assessed (e.g., previously removed or not removed for pathologic studies) |
| pN0 | No regional lymph node metastasis histologically, no additional examination for isolated tumor cells (ITC) |
| Note: ITC are defined as single tumor cells or small cell clusters not greater than 0.2mm, usually detected with immunohistochemistry (IHC) or molecular methods but that may be verified with H&E stains. ITCs do not usually show evidence of metastatic 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 > 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) |
| pN1mil | Micrometastasis (>0.2 mm, none > 2 mm) |
| pN1 | Metastasis in 1-3 axillary lymph nodes and/or internal mammary nodes with microscopic disease detected by sentinel lymph node dissection but not clinically apparent |
| pN1a | Metastasis in 1-3 axillary lymph nodes |
| pN1b | Metastasis in internal mammary lymph nodes with microscopic disease detected with sentinel lymph node dissection but not clinically apparent |
| pN1c | Metastasis in 1-3 axillary lymph nodes and in internal mammary lymph nodes with microscopic disease detected with sentinel lymph node dissection but not clinically apparent (if associated with >3 positive axillary lymph nodes, the internal mammary nodes are classified as pN3b to reflect increased tumor burden) |
| pN2 | Metastasis |
| pN2a | Metastasis in 4-9 axillary lymph nodes in clinically apparent internal mammary lymph nodes in the absence of axillary lymph node metastasis |
| pN2b | Metastasis in clinically apparent internal mammary lymph nodes in the absence of axillary lymph node metastasis |
| pN3 | Metastasis to > 10 axillary lymph nodes, in infraclavicular lymph nodes, or in clinically apparent ipsilateral internal mammary lymph nodes in the presence of > 1 positive axillary lymph nodes; or in > 3 axillary lymph nodes with clinically negative microscopic metastasis in internal mammary lymph nodes; or in ipsilateral supraclavicular lymph nodes |
| pN3a | Metastasis in > 10 axillary lymph odes (at least 1 tumor deposit > 2.0 mm) or metastasis to the infraclavicular lymph nodes |
| pN3b | Metastasis in clinically apparent 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 microscopic disease detected with sentinel lymph node dissection but not clinically apparent |
| pN3c | Metastasis in ipsilateral supraclavicular lymph nodes |
| DISTANT METASTASIS (M) | |
| Mx | Distant metastasis cannot be assessed |
| M0 | No distant metastasis |
| M1 | Distant metastasis |
