Lymph Nodes

As discussed above, the assessment of regional lymph nodes in a surgical cancer resection requires sufficient numbers to be able to comment on the absence of regional metastases and also the highest pN category, i.e. the total node yield and the number involved are important. In gastric carcinoma this means sampling and examining up to 15 regional nodes. Thus, node yields can be used to audit both care of dissection by the pathologist, adequacy of resection by the surgeon and the choice of operation, e.g. axillary node sampling vs. clearance. All nodes in the specimen should be sampled and, although ancillary techniques exist (e.g. xylene clearance, revealing solutions), there is no substitute for time spent at careful dissection with a preparedness to revisit the specimen after discussion at the multidisciplinary meeting. Care should be taken not to double-count the same node. Sometimes minimum target yields can be used—eight nodes will detect the vast majority of Dukes' C col-orectal carcinomas. The pathologist should also remember to count those nodes in the histological slides that are immediately adjacent to the tumour, as they are sometimes ignored yet more likely to be involved.

What is a node?

— a lymphoid aggregate >1 mm diameter with an identifiable subcapsu-lar sinus.

— direct extension of the primary tumour into lymph nodes is classified as a lymph node metastasis (TNM rule).

— a tumour nodule in the connective tissue of a lymph drainage area without histological evidence of residual lymph node is classified in the pN category as a regional lymph node metastasis if the nodule has the form and smooth contour of a lymph node (having first ensured that it does not represent tumour in a venule). A tumour nodule with an irregular contour is classified in the pT category, i.e. as discontinuous extension. It may also be classified as venous invasion (V classification), either microscopic (V1) or macroscopic (V2), as this is its likely origin.

Note that this differs from the 5th edition TNM classification, in which a connective tissue drainage area nodule <3 mm was designated as discontinuous extension and >3mm as a nodal metastasis. Although this change probably more accurately reflects biological events, it has caused discussion in the UK with concerns over observer reproducibility of the TNM 6 rule and inconsistency with on-going international trials. The resolution of this issue awaits further studies.

When size is a criterion for pN classification, e.g. breast carcinoma, measurement is of the metastasis, not the entire node (TNM rule). Size is also the whole measurement of a conglomerate of involved lymph nodes, and includes perinodal tumour.

Micrometastases

The significance of nodal micrometastases <2mm (designated (mi), e.g. pN1 (mi)) and isolated tumour cells (ITC) <0.2 mm (designated (i+), e.g. pN0 (i+)) demonstrated by immunohistochemistry is not resolved. In practical terms an accommodation within available resources must be made. Most busy general laboratories will submit small nodes (<5mm) intact or bisected, and a mid-slice of larger ones. Additional slices may be processed as required if the histology warrants it. Sometimes there is circumstantial evidence of occult metastases, e.g. a granulomatous response that will promote the use of immunohistochemistry in the search for single cell spread. The prognostic significance of micrometas-tases has yet to be clarified for the majority of cancers, e.g. a search for micrometastases is advocated by some in breast and colorectal carcinoma but considered to be of equivocal significance in oesophageal carcinoma. This area needs further clarification from large international trials which examine clinical outcome related to the immunohistochem-ical and molecular (reverse transcriptase-polymerase chain reaction, RT-PCR) detection of minimal residual disease in lymph nodes and bone marrow samples considered tumour-negative on routine examination. Detection by non-morphological techniques such as flow cytometry or DNA analysis is designated (mol+), e.g. pN0 (mol+) or pM0 (mol+) in lymph node or bone marrow, respectively. In the interim, the rationale behind assigning (i+) and (mol+) to the pNO category is because they do not typically show evidence of metastatic activity, e.g. proliferation, stromal reaction or penetration of vascular or lymphatic sinus walls.

Limit node

The limit node is the nearest node(s) to the longitudinal and/or apical resection limits and suture ties. Some specimens, e.g. transverse colon, will have more than one and they should be identified as such.

Extracapsular spread

Extracapsular spread is an adverse prognostic sign and an indicator for potential local recurrence (bladder cancer), particularly if the spread is near to or impinges upon a resection margin, e.g. axillary clearance in breast carcinoma. Perinodal tumour is also included in measurement of metastasis maximum dimension.

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