Table 5. Definition of Pathologic Regional Lymph N Categories.
| Stage | Definition |
|---|---|
| pNX | Regional lymph nodes cannot be assessed (e.g., not removed for pathological study or previously removed) |
| pN0 | No regional lymph node metastasis identified or ITCs only |
| pN0 (i+) | ITCs only (malignant cell clusters no larger than 0.2 mm) in regional lymph node(s) |
| pN0 (mol+) | Positive molecular findings by reverse transcriptase-polymerase chain reaction; no ITCs detected |
| pN1 | Micrometastases; or metastases in 1–3 axillary lymph nodes; and/or clinically negative internal mammary lymph nodeswith micrometastases or macrometastases by sentinel lymph node biopsy |
| pN1mi | Micrometastases (approximately 200 cells, larger than 0.2 mm, but none larger than 2.0 mm) |
| pN1a | Metastases in 1–3 axillary lymph nodes, at least one metastasis larger than 2.0 mm |
| pN1b | Metastases in ipsilateral internal mammary sentinel lymph nodes, excluding ITCs |
| pN1c | pN1a and pN1b combined |
| pN2 | Metastases in 4–9 axillary lymph nodes; or positive ipsilateral internal mammary lymph nodes by imaging in absenceof axillary lymph node metastases |
| pN2a | Metastases in 4–9 axillary lymph nodes (at least one tumor deposit larger than 2.0 mm) |
| pN2b | Metastases in clinically detected internal mammary lymph nodes with or without microscopic confirmation; with pathologically negative axillary lymph nodes |
| pN3 | Metastases in 10 or more axillary lymph nodes; or in infraclavicular (level III axillary) lymph nodes; or positiveipsilateral internal mammary lymph nodes by imaging in presence of one or more positive level I and II axillary lymphnodes; or in more than 3 axillary lymph nodes and micrometastases or macrometastases by sentinel lymph node biopsyin clinically negative ipsilateral internal mammary lymph nodes; or in ipsilateral supraclavicular lymph nodes |
| pN3a | Metastases in 10 or more axillary lymph nodes (at least one tumor deposit larger than 2.0 mm); or metastases to infraclavicular (level III axillary lymph) nodes |
| pN3b | pN1a or pN2a in presence of cN2b (positive internal mammary lymph nodes by imaging); or pN2a in presence of pN1b |
| pN3c | Metastases in ipsilateral supraclavicular lymph nodes |
ITCs = isolated tumor cells