Tumour Margins: A Pathologist’s Perspective

What is a tumour margin?
The question ‘Are the margins clean? Are there dirty margins?’ is one of the most important questions that a pathologist needs to answer when examining surgically- resected tumour tissue. Unfortunately, although an easy and straightforward question to ask, it is not always as easy to answer it, particularly when dealing with anatomically- complex sites.

A ‘tumour margin’ or ‘surgical margin’ is the strip of non- neoplastic tissue between the edge of the tumour and the surgeon-cut surface. The ‘surgeon-cut surface’ is the edge of the tissue that has been physically cut/dissected by the surgeon. The surgeon can greatly assist the pathologist by inking the surgeon-cut surfaces of the tissue specimen prior to submission, so that the true surgeon-cut surface can be readily identified in the laboratory. The benefits of this are discussed below.

The vast majority of the published studies do not describe how a tumour was examined in the histopathology laboratory or indeed how it was determined that the mass was or was not fully excised. This is a key point to remember when critically reading such studies as there is no universal definition of what is a ‘clean surgical margin’. If the method of margin examination is not defined in the study, then any results should be interpreted with caution.

Sampling a tissue specimen to assess the adequacy of surgical excision:
The entire tissue cannot be examined histologically unless the tissue is tiny and therefore any histological evaluation of a tumour sample involves some pragmatism and degree of judgement as to which of the many orientations or planes of sections are the most likely to provide the clinically-relevant information.  [...]