Resection Margins

Status of proximal, distal and radial margins and their distance from the invasive carcinoma must be specified. The circumferential (radial or lateral) margin is the most critical for rectal tumours, because of the high risk of local recurrences. In terms of survival: a positive margin increases the risk of local recurrence 3.5-fold and doubles the risk of death from disease [51]. This margin represents the adven-titial soft tissue margin resected by surgery. Careful routine assessment of the non-peritonealised surfaces of the "fresh" specimen throughout its entire length is needed to assess the completeness of mesorectal resection. Macroscopic pathologic assessment of the completeness of the mesorectum of the specimen accurately predicts both local recurrences and distant metastasis [52] (Table 3) (Fig. 4). Mesorectal resection can be scored as complete, partially complete or incomplete [53]. Microscopic evaluation of the radial margin may be difficult on histo-logic sections and it may be helpful to mark the surface with ink before formalin fixation [25] (Figs. 5, 6).

Routine assessment of the distance between the tumour and nearest radial margin (i.e., "surgical

Fig. 4a, b. Macroscopic assessment of the completeness of the mesorectum. a Nearly complete. Irregularity of the surface of mesorectal envelope (fresh specimen). b Complete. Only minor irregularities of the surface of mesorectal envelope (smooth surface) (fresh specimen)
Fig. 5a, b. Mesorectal envelope. a Non-peritonealised back surface. b Margin marked with ink

clearance") is mandatory [21]. The circumferential margin is scored as positive if the tumour is located 1 mm or less from the inked non-peritonealised surface of the specimen [25] (Fig. 7). This includes tumour within a lymph node as well as direct tumour extension (if positivity is based solely on intranodal tumour, this should be stated). The distance (in mm) of the tumour from the margins, should be present in the pathologic report as it helps to assess the adequacy of surgical resection and identifies patients for adjuvant therapy [54-56].

The quality of the surgical technique is a key factor in the success of surgical treatment for rectal cancer, both in the prevention of local recurrence and in long-term survival. Total mesorectal excision (TME) improves local recurrence rates and corresponding survival by as much 20%. This surgical technique entails precise sharp dissection within the areolar plane outside (lateral to) the visceral mesorectal fascia in order to remove the rectum. This plane encases the rectum, its mesentery, and all regional nodes. High-quality TME surgery reduces local recurrence from 20 to 30%, 8 to 10% or less, and increases 5-year survival from 48 to 68% [57-61].

Moreover, the distance of the tumour from proximal and distant margins should also be assessed in millimetres: these measurements represent disease-free colon segments. A positive longitudinal margin, usually the distal one, is considered to be a negative prognostic factor: this margin should be evaluated on the fresh specimen to avoid retraction due to fixation. A macroscopic evaluation is possible because colorectal carcinomas rarely have an intramural spread beyond the macroscopic margins. Anasto-motic recurrences are rare when distance of the tumour from these margins is greater than or equal to 5 cm. For neoplasia of the lower rectum treated by low anterior resection, a 2-cm margin is considered adequate [62].

There is a special system to describe tumour remaining in a patient after therapy with curative intent, namely R classification (Table 4). For the surgeon, the R classification indicates the assumed status of the completeness of a surgical excision; for the

Fig. 7a, b. Radial margin of rectal cancer. a Cross-section through the bowel and radial margin: fresh specimen. b Tumour is not present in the radial margin

Table 4. R classification: residual tumour

Rx: presence of residual tumour cannot be assessed R0: no residual tumour R1: microscopic residual tumour R2: macroscopic residual tumour pathologist it is relevant to the status of the margins of a surgically resected specimen. The completeness of resection is dependent in large part on the radial margin. R0 suggests complete tumour resection with all margins negative, R1 is an incomplete tumour resection with microscopic involvement of a margin and R2 is an incomplete tumour resection with macroscopic involvement of a margin and gross residual tumour that was not resected.

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