Colorectal carcinoma: histopathological diagnosis and staging

Abstract

It is possible to make a histopathological diagnosis of colorectal carcinoma from ulcerating lesions by means of forceps biopsy, but this presents problems in polypoid tumours. In order to make the diagnosis of invasive carcinoma, evidence of invasive growth into the submucosa is necessary. In polypoid tumours, this can be done usually only by endoscopic or surgical polypectomy. In addition to histopathological diagnosis, one of the most important tasks for the contemporary pathologist is the exact classification of colorectal tumours. The most important parameters are typing, grading, staging and the R classification, i.e. the assessment of presence or absence of residual tumour following treatment. Typing and grading is done according to the WHO recommendations; the great majority of colorectal carcinomas are adenocarcinomas or mucinous adenocarcinomas. In grading, one can differentiate into either four grades (G1 to 4) or between low and high grade. The internationally accepted TNM/pTNM system, as described in the 4th edition, is used for staging. This system has considerable advantages over the traditional, but often misused Dukes' classification. After treatment, the surgeons and the pathologists must work together to determine the R classification. Typing, grading and staging are of great importance in deciding on the indication for either a limited surgical procedure or a radical resection. Together with the R classification, they decisively influence the indications for post-treatment after surgical therapy. R classification is the most important factor for prognosis after surgical removal of tumours. Following resection for cure, the prognosis is especially affected by the pTNM classification and its corresponding stages. The independent prognostic significance of other clinical, macroscopic and histological findings cannot yet be definitively determined.