Excision Margins

The clearance of excision margins has important implications for patient follow-up, adjuvant therapy and local recurrence of tumour. Positive resection margins in a breast cancer may mean further local excision, conversion to a total mastectomy and/or radiotherapy to the affected area. Measurements should be made on the gross specimen, checked against the histological slide and verified using the stage micrometer or eyepiece graticule. A very useful practical aid is a hand-held perspex dome magnifier that contains an in-built graduated linear scale. Painting of the margins by ink supplemented by labelling of the blocks is important. Paint adheres well to fresh specimens but also works on formalin-fixed tissue. India ink or alcian blue are commonly used. Commercially available multi-coloured inks are helpful, particularly if there are multiple margins as in breast carcinoma. The relevance of particular margins varies according to specimen and cancer type.

1. Longitudinal margins. Involvement can be by several mechanisms:

(a) Direct spread. In rectal carcinoma the longitudinal margin in an anterior resection is considered satisfactory if the anastomosis is 2-3 cm beyond the macroscopic edge of the tumour, i.e. direct longitudinal spread is minimal. However, there may be involvement if the tumour is extensively infiltrative, poorly differentiated or of signet ring cell type, or shows prominent LVI. Appropriate limit blocks should be taken. In addition to the resection specimen limits, separate anastomotic rings are also usually submitted.

(b) Discontinuous spread. In oesophageal and gastric carcinoma there is a propensity for discontinuous lymphovascular submucosal and mural spread, and margins should be checked microscopically even if some distance from the primary tumour.

(c) Multifocal spread. In transitional cell carcinoma of the urinary tract, malignant lymphoma of the bowel and papillary carcinoma of the thyroid, potential multifocality must be borne in mind.

2. Circumferential radial margin (CRM). An often ignored measurement, these margins are assuming increasing importance in relation to local recurrence and morbidity, e.g. mesorectal CRM and rectal carcinoma. It is recommended practice to measure how far the carcinoma has spread beyond the organ wall and how far it is from the CRM. Other examples are: oesophageal carcinoma and the adventitial margin, cervical carcinoma and the parametrial margin, renal carcinoma and the perinephric fat/fascial margin. Lymph node metastasis at a CRM is also considered positive. The significance of some other examples is less well defined but comment should be made, e.g. the mesenteric edge in colonic carcinoma.

3. Quadrant margins. Examples are a skin ellipse for carcinoma or malignant melanoma. Usually the longitudinal axis margins are well clear and the nearest to the tumour are the transverse axis and deep aspects. It is important to check clearance not only of the infiltrating tumour but also adjacent field change, e.g. epidermal dysplasia or radial spread of a malignant melanoma. Actual measurement of margin clearance can be important in assessing the need for further local excision, e.g. malignant melanoma. An alternative technique is multiple serial transverse slices demonstrating the entirety of the transverse axis margins with the longitudinal axis tips also embedded in toto ("toast-racking").

4. Serosa or peritoneum. This is a visceral margin and breech of it allows carcinoma to access the abdominal and pelvic cavities. Its importance has been re-emphasized, as for example at the upper anterior aspect of the rectum where there is potential for peritoneal disease as well as local mesorectal recurrence posterolaterally. Standard practice may also involve measuring the distance from the invasive edge of the tumour to the serosa, e.g. uterine adenocarcinoma.

Colonic carcinoma: serosa; prognostic distinction is made between carcinoma in a subserosal inflammatory reaction (pT3) and carcinoma being at and ulcerating the serosal surface (pT4).

5. Multiple margins. As in breast carcinoma (lateral/medial, superior/ inferior, superficial/deep), this requires differential painting and block labelling, according to a previously agreed protocol for specimen orientation markers, e.g. surgical sutures. Alternatively, the surgeon may submit multiple site oriented shave margins marked as to their inner and outer (new in-vivo margin) aspects.

6. Involvement. Inadequate clearance of excision margins varies according to the tissues and tumours concerned:

Breast carcinoma: invasive, <5mm; in-situ (ductal), <10mm Rectal carcinoma: mesorectum, <1 mm (either by direct extension or discontinuous in a node or lymphovascular channel).

TNM resection classification

R residual tumour

Rx presence of residual tumour cannot be assessed

R0 no residual tumour

R1 microscopic residual tumour (proven by tumour bed biopsy or cytology) and in effect if tumour involves (to within <1 mm) the resection margin

R2 macroscopic residual tumour.

Residual disease takes into consideration not only locoregional tumour but also any remaining distant metastases. It can also be applied following surgery, radiotherapy or chemotherapy, alone or in combination. For a number of tumour sites there are also semiquantitative histologi-cal regression grading systems applicable to post multimodal treatment.

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