Diagnostic Pathology

The preliminary report will consist of examination of the unfixed specimen by both surgeon and pathologist at the time of surgery; preferably intra-operatively with direct communication between surgeon and pathologist. The distinction between a low sigmoid and high rectal cancer can be difficult. This is important to balance the increased toxicity associated with radiating high lesions (because of injury of surrounding bowel) with the recurrence risk within the pelvis. If the tumour lies below the peritoneal reflection it is generally considered a rectal cancer for the purposes of adjuvant therapy considerations. Proximal and distal resection margins should be noted. Location of the cancer relative to the peritoneal reflection should be noted. The apex of the mesenteric resection at the proximal tie marking the superior rectal or inferior mesenteric artery should be identified and the presence or absence of gross lymphadenopathy should be noted. The specimen should be marked to allow histologic examination of the radial circumferential margin. The closest radial margin should be noted and marked; the closest radial margin should be oriented as to anterior, posterior, left and right.

The histologic report will consist of examination of the fixed specimen and should include reporting of the cell type and degree of differentiation, the maximal depth of penetration by the cancer cells, the proximal and distal margins, the circumferential margins including distance to the nearest radial margin, involvement of lymphatics and blood vessels at the proximal, distal, and apical mesenteric margins, and examination and reporting on at least 12 lymph nodes as recommended by TNM (UICC) and AJCC¹. Consideration should also be given to reporting the closest radial margin of lymph node metastasis of the edge of the mesorectal fascial envelope (2). The finding of non-lymph node deposits within the mesorectum have the same prognostic significance as involved lymph nodes and these deposits are recorded as node deposits in the staging of the primary cancer. Patients with no identified nodes have a higher recurrence risk than those with examined nodes that are negative.

The vast majority of colorectal malignancies are adenocarcinomas. Rarer entities (carcinoid, etc) are dealt with in other sections of this manual. On occasion, therapy may be influenced by knowledge of the degree of differentiation present. The presence or absence of lymphatic and vascular invasion in the region of the tumour is increasingly thought to be of importance and may also ultimately determine the need for adjuvant therapy.

Final stage assignment

The surgeon and pathologist should agree on the likelihood of the presence or absence of pelvic residual disease based on gross and histologic examination of the proximal, distal and radial resection margins.

The surgeon should assign the postoperative pathologic stage in light of findings from metastatic investigation, laparotomy, and pathology reporting.

References:

1. Goldstein NS, Sanford W, Coffey M, Layfield L, Lymph node recovery from colorectal resection specimens removed for adenocarcinoma: trends over time and a recommendation for a minimum number of lymph nodes to be removed. Am J Clin Path 1996; 106:209-216.
2. Quirke P, Durdey P, Dixon MF, Williams NS, The prediction of local recurrence in rectal adenocarcinoma by histopathological examination. Lancet 1986; 2:996-999.