[Colorectal carcinoma--diagnostic requirements from the clinical point of view]

More than 90% of colorectal cancers develop from adenomas (adenoma-cancer-sequence). An adequate preoperative diagnosis must include the tumour classification: 1. Typing = identification of the tumour type (by histology), 2. Grading = degree of differentiation and malignancy (by histology), 3. Staging = anatomical spreading of the tumour (preoperative: clinically, postoperative: following the TNM classification). Therefore, an exact preoperative tumour classification needs an endoscopic and histologic examination. Radiology does not fulfil these criteria and remains a complementary method only. In adenomas with severe cell atypia and in adenomas with invasive cancer with few exceptions (degree of malignancy 3, signet ring cell carcinoma, undifferentiated cancer) polypectomy (by snare or surgically) is the method of choice. Only when the excision cannot be performed totally or a lymphatic infiltration is proven radical operation has to be done subsequently. In cases of advanced colorectal cancer only total colonoscopy with forceps-biopsies ( = typing, grading) and clinical staging with ultrasonography (liver metastases) is essential. Examination of the entire colon is decisive for preoperative diagnosis (metachronous cancer in 1,6%, additional premalignant lesions up to 20%).