<http://www.bccancer.bc.ca/HPI/CancerManagementGuidelines/Gastrointestinal/05.Col
on/5Diagnosis.htm>

1) Clinico-pathologic Considerations

The diagnosis of colorectal cancer is based upon biopsy usually achieved
at sigmoidoscopy or colonoscopy. It is particularly important that the
clinician define the level at which the cancer is found, as this may
have important bearing on subsequent surgical and adjuvant therapy. Any
patient with a diagnosis of colorectal cancer should have a complete
evaluation of the entire colon, preoperatively where possible, because
of the increased risk of finding additional polyps or cancers.

2) Diagnostic Pathology

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 contribute to the
determination of the need for adjuvant therapy.

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 of the bowel wall ,
the proximal and distal margins, the circumferential margins,
involvement of lymphatics and blood vessels at the proximal, distal, and
apical mesenteric margins, and examination and reporting on lymph nodes
(preferably at least 6-12).

Non-lymph node deposits within the pericolic fat 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
in whose specimens no lymph nodes are identified have a higher
recurrence risk than those with no involved nodes, probably by virtue of
understaging.