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