Surgical margins

A positive surgical margin (ink on tumour) in urothelial carcinoma. H&E stain.

A positive surgical margin (tumour with cautery artifact) in colorectal carcinoma. H&E stain.

The surgical margins, often simply referred to as margins, are the set of surfaces that were cut by the surgeon in order to remove the specimen from the body. The distance between the tumour and the margin is called the surgical clearance, a term that may be used interchangeably with the term surgical margin. Margins are important as an incompletely removed disease process may lead to re-occurrence.

What defines a positive surgical margin is dependent on the tumour and its biology; the definitions for a positive margin are often dependent on (1) the anatomical site of the tumour and (2) the tumour type.

Significance

Most often, positive margins, i.e. surgical margins with disease present or "very close", are non-optimal. For example, in locally advanced rectal cancer, in one study, five year survival was found to be 60%, 31% and 0% for R0 (no tumour at the margin), R1 (microscopic tumour at the margin), and R2 (macroscopic tumour at the margin) resections respectively.

Types of margins

• En face (formally en face margin).
  • Sample the complete surface.
  • No information about the distance between the margin and lesion can be obtained at microscopy, i.e. from the glass slide.
• On edge (formally on edge margin), AKA perpendicular margin, as the cut to prepare the tissue for microscopic examination is perpendicular to the cut from the surgeon.
  • Sample a subset of the surface.
  • The distance between the margin and lesion can be measured at microscopy, i.e. on the glass slide.

Note:

• It should always be clear from the gross description which type of margin was taken; this is especially important for cases that were not submitted in total.

Positive margin definition

Unfortunately, there is no universal definition for positive margin.

Definitionally, there is agreement that "tumour touching the edge of the specimen" is a positive margin.

It may be useful to differentiate pathologic margin [status] (tumour touching inked margin) and oncologic margin [status] (tumour sufficiently clear of margin to not significantly affect the prognosis). Oncologists, surgeons and patients really only care about oncologic margin [status] for relatively obvious reasons.

Perhaps confusing is that: a [pathologically] clear margin may be defined as being [oncologically] a positive margin, e.g. tumour not touching the ink of an inked margin - but less than 1 mm from the ink - may be a "positive margin".

Adequate margin

• What constitutes an adequate margin is dependent on the tumour type, as different tumours have different behaviours.

Adequate margins by tumour

Tumour	Adequate pathologic margin	Adequate clinical margin	System
Colorectal carcinoma	>1 mm; circumferential margin (esp. in rectal carcinoma) most important	1 cm	Gastrointestinal pathology
Vulvar carcinoma	0.8 cm (fixed)	1.0 cm (fresh)	Gynecologic pathology
Malignant melanoma	same as clinical (interesting is that CAP says "no minimum safe distance established")	MIS: 5 mm considered inadequate by some <2 mm invasion: 10 mm >=2 mm invasion: 20 mm	Dermatopathology
Ductal carcinoma in situ	ink cannot be on tumour - consensus of Society of Surgical Oncology-American Society for Radiation Oncology (for low stage tumours)		Breast pathology
Invasive breast carcinoma	ink cannot be on tumour - consensus of Society of Surgical Oncology-American Society for Radiation Oncology (for low stage tumours)		Breast pathology
Sarcoma	>= 1 cm		Sarcoma
Prostate carcinoma	tumour not touching ink - "close" margins have a higher biochemical recurrence		Genitourinary pathology
Renal cell carcinoma	tumour not touching ink; positive margins get clinical follow-up as recurrences are uncommon		Genitourinary pathology
Squamous cell carcinoma of the skin		4 mm, 6 mm for high risk	Dermatopathology
Urothelial carcinoma	tumour not touching ink		Genitourinary pathology

Fragmented and incised specimens

There is limited advice on how to deal with a fragmented or incised specimen.

If the specimen can be "put back together", it is reasonable to assess the margin and comment on the limitation.

The College of American Pathologists synoptic for invasive breast carcinoma (version 4.3.0.1) states:

If the specimen is received sectioned or fragmented, this should be noted, as this will limit the ability to evaluate the status of margins.

Microscopic

Features of the true margin:

• Irregular/non-linear appearance.

DDx:

• Cut at the grossing bench (by the pathologist/pathology assistant/pathology resident) post-fixation - these are usually straight.
• Artifactal cleft/separation.

Note:

• The surgeon's cut is irregular due to loading during extraction and fixation effects.

Images

• 

  True margin - surgeon's cut (left of image) - extremely low mag. (WC)

• 

  Pathology assistant's cut (right of image) - extremely low mag. (WC)

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Stray ink versus true positive

True positive

COMMENT: 
Ink is seen very focally on a fragment of tumour in A21-1. Inspection of 
the tissue block shows ink on the surface of the tissue fragment with the 
positive margin; this essentially excludes that what is interpreted as a 
positive margin could represent stray ink.

Stray ink

COMMENT:
The margin assessment is suboptimal as the specimen was cut prior to 
inking. Ink on tumour in this context may represent stray ink on tumour 
or a true positive margin. 

Ink is focally present on tumour in this case and it is favoured to 
represent stray ink, as the quantity of ink is minimal; however, margin 
positivity cannot be completely excluded.

A re-excised (previously) positive margin is negative for tumour

It occasionally happens that a re-excised margin specimen is negative for tumour.

The lack of tumour in Part B may be explained by either of the following:
(1) There was minimal clearance (<1 mm) in Part A that was not sampled. 
(2) The sampling of Part B missed minimal tumour involvement. 

Note:

• One should review the positive margin call to ensure it isn't an overall.

Tumour in tip - flipped block

Lesion, Right Upper Lid, Excision:
     - BASAL CELL CARCINOMA, favour clear margin (see comment).

Comment:
Basal cell carcinoma (BCC) is present in the block 3 tip, on the initial cut. The tissue was re-embedded and BCC is seen on the recut. BCC is clear of the inked margin. Thus, the margin is favoured to be clear; however, out-of-plane margin involvement cannot be excluded.

Alternate

Lesion, Right Lower Eyelid, Excision:
     - BASAL CELL CARCINOMA (BCC), cannot exclude positive margin, see comment.

Comment:
BCC was found in block 1 (one of the tips) on the initial cut.

In block 1, BCC is present but distant from the inked margin in the plane 
of section. The margin is not completely in the plane of section; thus, 
trimming of a negative margin cannot be entirely excluded. As BCC is seen 
on both sides of the block, a positive cannot be excluded.

See also

• Basics.
• Frozen section.
• Crush artifact.
• Marking ink.