The assessment of surgical margins in the reporting of submissions of neoplasia is critical to the decision-making in treatment and management of clinical patients. The assessment of margins helps the surgeon and veterinarian or oncologist determine if local control has been achieved with a high degree of certainty. Good communication between the clinician, surgeon, laboratory technologist and pathologist will greatly improve the information provided, ensure that the samples are evaluated correctly and the appropriate decisions are made for the patient by the owner.
There is a real dicotomy with what is expected in margin assessment. Primary care veterinarians have different expectations to secondary or tertiary care practices.
A. Medical and surgical oncologists expect three things about margin assessment from the pathologist and their reports . They are
- relationship of the neoplasm to the surrounding tissue
- presence (or absence) of tissue barriers that define the compartment in which the tumor grows
- measurement of the distance from neoplastic cells to an inked margin (called the histologic tumor free distance or histologic tumor free margin width)
Words such as 'complete', 'clean', or 'clean but close' are often considered to be absolute, suggesting 100% certainty that excision will be curative. This is far from the truth. The probability that local control will be obtained is an assessment that is most accurately made by the surgeon. The surgeon takes into account the original surgical dose, anatomical location, known behaviour of the neoplasm, surgical technique, presence of compartment boundaries and post surgical tissue shrinkage, to name several.
B. Primary care veterinarians rely on the pathologist for advanced knowledge about prognosis and margins. Primary care practice is changing so that more and more, complex surgery is done by specialist surgeons, or those who have advanced skills. They have advanced expectations. Routine surgery in primary care is now removal of skin tumors. Epithelial tumors of skin are usually local only and require narrow margins to completely remove the local disease. Potentially invasive or known invasive tumors require wide margins to increase the probability of a local cure. This wide margin should include the tissue barriers that define the compartment in which the tumor is growing, and if there is no boundary, a wide surgical margin as defined by the surgeon.
Pathologists want to be helpful. They know the submitting primary practice veterinarian looks to them for prognosis, and to assess the margins. The primary care veterinarian wants to know if the margin is clear, clean or excision is complete. Many pathologists actually say 'margin is clear', 'margin is complete' or 'margin is clean'. What they are really saying is that they can see normal tissue between the neoplastic cells and the surgical margin in the section before them. Some pathologists use 'complete' or 'clean' if the distance between neoplastic cells and the surgical margin is 1 mm. Some use 3 mm. So there is no accepted definition of clear, clean, complete.
If a pathologist says that the excision is complete or the margin is clean, does this mean the margin is adequate or appropriate? NO. To assess margin adequacy or appropriateness, one must know clinical features (like how rapid was growth, how fixed the mass is to the surrounding tissue, its exact location, proximity to compartment barriers ('fascial planes'), proximity to sensitive structures, and many other facts that only the clinician knows.
Veterinarians, do your own interpretation based on data. If the pathologist does not provide the important data (relationship to surrounding tissue, histologic tumor free distance, and compartment barriers) ask for it!
Surgical intent or dose
The surgeon should always provide a description of the intent of surgery be it curative or not. Incisional or intralesional biopsy or cytoreductive (debulking) surgery, and even marginal incision is not always intended to be curative. The expectation with a curative intent surgery is for the pathologist to report margins. Incisional or intralesional biopsy is for diagnosis and is usually done in combination with cytology. Cytoreductive surgery is for diagnosis and debulking. Debulking is to attempt to reduce the local tumor to microscopic neoplasia only. Once debulked, additional surgery can be planned, or adjunctive therapy such as radiation and or chemotherapy can be done to treat microscopic disease. Pathologists should no report margins for incisional or intralesional biopsy.
Marginal excision is a common routine surgery in many primary care practices. Marginal excision is defined by Enneking et al (1980) as a surgery that removes the mass in one piece, and the plane of dissection is "through the pseudocapsule or reactive tissue about the lesion, and when performed for malignant lesions, leaves microscopic disease". It should not be used for curative intent unless the neoplasm is known to have a capsule. Surgical oncologists use this technique typically for neoplasms near vital structures or when the aim is to cytoreduce the neoplasm. Pathologists should report margins in these cases unless the surgeon indicates they know there is residual disease.
Curative intent surgery is to attempt a remove the local disease with the highest probability of achieving a local cure, given the circumstances. 'Wide' and 'radical' excision may be used depending on the neoplasm and the region in which it is located.
There are varying definitions for what constitutes a marginal, wide or radical incision, so it is best to communicate the intent of surgery and the planned distance from the tumor that the surgical incision is made.
Inking margins
It is best for the surgeon to ink the surgical margins to be assessed, and to indicate any specific questions or areas of concern. Many laboratories have a standard operating procedure to ink margins that are not already inked.
Inking of margins is best done with fresh tissue that has the surface dried with a paper towel or absorbent material. Ink designed for the purpose (tattoo ink can also be used) should be painted on the surgical site, allowed to air dry, and then fixed. Neoplastic tissue should not be incised prior to or after application of ink. Careful description of the site, location and color of applied ink should be made. The submission form should be explicit in the exact requirements of the surgeon.
Evaluate surgical margins
It is the responsibility of the surgeon to evaluate the pathology report in light of the surgery performed and determine whether the margins reported by the pathologist are adequate for the neoplasm. Adequacy or appropriateness of excision can only be determined by the surgeon. This is because the surgeon is the one who knows how fast the neoplasm is growing, the exact location of the mass, relationship of the mass to adjacent structures, potential presence or absence of a tisseu barrier (fascial plane), the limitations of the surgery based on critical structures, sufficient skin to close the wound, and on the healing characteristics of that region. At surgery, the surgeon should plan for a margin of a certain distance. This plan encorporates an assessment of the compartment in which the neoplasm is growing. This compartment is bounded by barriers - these barriers vary in effectiveness. When there is no effective tissue barrier, normal tissue of a wide enough distance is taken instead. The pathologist must report the presence of the tissue barrier and the shortest distance the neoplastic cells are from the inked margin. This distance is called the histologic tumor free distance. The distance reported by the pathologist can be compared to the distance planned before surgery and the difference is included in the factors assessed for subsequent treatment. The category of R0, R1 and R2 (R stands for reoccurrence) is determined clinically by taking the measured margins and clinical factors.
In general, if neoplastic cells are present at any one margin, the whole surgical field is considered potentially contaminated. Subsequent attempted excision of ‘residual disease’ would involve complete removal of the initial surgical field plus any additional margin, or if radiation therapy is used, the entire surgical field including the scar would be included in the radiation field. This does not apply if completely different surgical instruments were used for individual margins. The inking of margins when different surgical instruments were used is best done by the surgeon, who will use different colours of ink. The surgeon will indicate which ink belongs to which location so the distance between neoplastic cells and each location can be determined. Application of sutures or staples can be done if the surgeon does not have a variety of coloured ink.
It is important that technicians who trim samples describe the sample including the sectioning technique (radial, parallel, tangential), how far the mass appears grossly from the margins (or not), and record from where the samples were taken, ink colors and any portions labelled by the surgeon. Labelled photographs or diagrams of submissions are a good way of doing this.
The distance between neoplastic tissue and a margin is best measured by knowing that the margin observed histologically is in fact the surgical margin. Inking of the surgical margin is the way to achieve this. Most laboratories have, as their standard operating procedure, inking of surgical margins of submitted tissue. Inking of surgical margins should be performed by the surgeon prior to fixation when possible. This avoids the effects of variable tissue contraction. For example, skeletal muscle contracts during fixation and distorts that part of the surgical margin. The removal of fat from tissues during paraffin embedding will also shrink the tissue during fixation. This shrinkage varies up to about 25%. Inking can be done after fixation – and like inking of surgical specimens, requires painting the surface with the best ink. Since tissues may shift, if a surgeon has inked the specimen prior to fixation, it is important to observe the inked regions and not add additional ink after fixation. In many cases, deep margins will shift with loss of fat and they may no longer appear deep to the tumour after fixation.
The responsibility of the pathologist is to report, in order of importance,
- The interaction of the neoplasm and the surrounding tissue. This includes any capsule, expansile growth, compression of normal tissue, peripheral invasive growth, and lymphovascular invasion.
- The presence of effective or dense tissue or compartment barriers (fascial planes). An effective tissue barrier is a seemingly impenetrable band of tissue through which the neoplasm would not be expected to invade. Examples include aponeurosis, periosteum and bone, epimysium, epineurium, dura mater, dense collagen with the subcutaneous striated muscle layer, dense collagen overlying the rectus abdominous muscle, smooth muscle of the muscularis mucosa, the muscular tunic of the intestine and uterus and many others.
- The minimal or shortest distance between neoplastic tissue and the closest inked margin (histological tumor free distance). For skin and subcutaneous tumors this includes the lateral margin and the distance or type of tissue between neoplastic tissue and the deep margin. The difference between the distance that the pathologist reports, consideration for the amount of tissue shrinkage, and the intended or attempted margin that the surgeon planned, are all part of determining, by the surgeon, if the margin was adequate or appropriate.
Pathologists do not have the information required to interpret margins as being 'clean' or 'complete' in potentially infiltrative neoplasms, yet many do and can be wrong. A clean or complete margin (really it is the presence of a HTFD), as indicated by a pathologist, is done using microscopic assessment of extremely short distances, sometimes of the order of 0.1 mm (100 µm). This distance may not be adequate or appropriate and thus can give the surgeon an incorrect impression of the margin. It is best not to use these terms and instead to provide a comment on whether tumour cells are seen to touch or cross the margins in any sections, or the distance from the closest neoplastic cell to the margins. It is also important and essential to indicate if tumour cells penetrate through the compartment boundary/dense tissue barrier/fascial plane.
It is important for the pathologist to share with the surgeon how margin assessment is performed. The majority of laboratories sample masses by the radial method. For skin samples, 5 margins are assessed: 4 lateral margins taken in a radial pattern, and the deep margin. If the sample is small enough, this takes 3 pieces of tissue – a cut across the shortest diameter of the sample to obtain 2 lateral and 1 deep margin, and 2 additional pieces of tissue taken at right angles to the first cut. For large masses, this method will result in many regions along the lateral surgical margin not being assessed. As a result, the surgeon should indicate any areas of greater concern for assessment so the pathologist can more closely evaluated these regions.
Because the aim of obtaining an adequate margin is an assessment of the probability of achieving a local cure, it must be based on science - outcome based studies. Many of these studies have not been done!
There is no realistic “standard operating procedure” for determining adequacy or appropriateness of surgical margins in every case. Many neoplasms have unique characteristics, and individual characteristics, growth habit and life history is part of determination of appropriateness of margins. A 0.5 mm margin for the majority of follicular tumors is adequate for local control but a similar margin for a fibrosarcoma would oftentimes not be adequate.
Where to begin? Find out how far the client wants to go.
Systemic metastasis?
A neoplasm with a high liklihood of metastasis systemically will probably require staging, monitoring and systemic therapy for the best possible outcome.
Metastasis to a draining lymph node?
A neoplasm with a high liklihood of metastasis to a local lymph node will require local control at the site of the neoplasm and of the draining lymph node. Determining the draining lymph node using dyes helps when there are many potential draining nodes - like on the face or the pelvic perineal region.
Local therapy to ensure local control and nodal control is used here.
Local control is usually managed by surgery and or radiation. To do this you must know the answer to the following questions.
What kind of neoplasm are you dealing with?
Use cytology first. Many neoplasms can be diagnosed cytologically.
Then do either incisional biopsy (if cytology is not diagnostic) or curative intent surgery using the most likely diagnosis.
Neoplasms with a capsule or that are not infiltrative require marginal excisions.
Infiltrative neoplasms require wide or radical excision, depending on the presence of a fascial plane or abundant surrounding tissue.
What is the tissue compartment?
An effective tissue barrier (fascial plane) is a potential real barrier to infiltrating neoplastic cells. A tissue barrier (fascial plane) is a band of fibrous tissue, epimysium, aponeurosis, periosteium, muscle belly, bone, abdominal wall, or capsule. The Surgical Pathology Report MUST report on the presence of a compartment boundary. A tumor that does not penetrate a tissue barrier is considered to have adequate margins.
The boundary of a tissue compartment is a dense layer of collagen or collagenous tissue. There are different words used for this boundary. Some use the word fascial plane. Fascia is a latin word derived from 'fascis' meaning bundle. It is used to mean "a band, bandage, swathe, ribbon" and was first used in english from 1788 (see https://www.etymonline.com/search?q=fascia). When one is dealing with a word that was used for so long , and before widespread histological techniques about 1819, there is bound to be differences in understanding. These include any arrangement of fibrous connective tissue containing bundles of collagen. Interlobular septa of subcutaneous tissue, collagenous tissue surrounding organs, blood vessels and nerves. Fascia is the tissue that holds the body together and can be loosely arranged or dense tissue. In the context of a tissue compartment and to avoid confusion, it is best to use the term 'dense tissue barrier' rather than fascial plane.
Tissue barriers are barriers to spread of neoplastic cells or inflammation within the body. In a general sense, they can be any tissue that prevents spread. Some are more effective to others and there is an interplay between the type of invasion or spread and the degree of barrier function, so some tumors cannot invade some tissue but they can invade others. In the context of neoplasia and margins, tissue barriers are the boundaries of compartments.
No tissue barrier?
The lack of a fascial plane (typical for lateral margins of a skin mass) means the requirement for an appropriate HTFD. This could be 5cm, 3 cm, 2 cm, 1 cm or 1 mm depending on the known behaviour of the neoplasm, both in general and specifically for that patient.
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