[Colorectal cancer: classification and aspects of the proliferation kinetics]

The exact tumor classification by the pathologist is the basis of adequate therapy of colorectal carcinomas. The classification includes the determination of the histological type of the carcinoma and the grading according to the criteria of the WHO and the UICC, as well as the staging according to the TNM system of the UICC and the Dukes classification. Most colorectal carcinomas are adenocarcinomas of tubular, tubulo-papillary and papillary subtypes. Mucinous adenocarcinomas are characterized by a pronounced extracellular mucus production. Signet ring cell carcinomas with intracellular mucus production are very rare and predominantly localized in the right-sided colon. Adeno-squamous carcinomas and squamous cell carcinomas are extremely rare in the large bowel. They are only mentioned for completeness. The histological grading proposed by the WHO distinguishes carcinomas of well (G1), moderately well (G2) and poor (G3) differentiation. Well and moderately well differentiated tumors can be regarded as carcinomas with low grade of malignancy, whereas poorly differentiated ones are carcinomas with high grade of malignancy. The new grading of the UICC distinguishes in addition to the well, moderately well and poorly differentiated carcinomas the undifferentiated tumors (G4). G1 and G2 correspond to low grade, G3 and G4 to high grade of malignancy. According to the 1987 nomenclature of the UICC-TNM system pT1 denotes tumor spread to the mucosa, or mucosa and submucosa, pT2 to the muscularis propria, pT3 into the subserosa or into nonperitonealized pericolic or perirectal tissue and pT4 a perforation of the visceral peritoneum or a spread into other organs.(ABSTRACT TRUNCATED AT 250 WORDS)