Pathology of Rectal Cancer
Treatment of rectal cancer requires an interdisciplinary approach, with imaging techniques and morphological examination playing important roles. The pathologist is involved in several steps of diagnostics and treatment planning for patients with rectal t
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Pathology of Rectal Cancer Thorsten Wiech and Martin Werner
3.1 Introduction Treatment of rectal cancer requires an interdisciplinary approach, with imaging techniques and morphological examination playing important roles. The pathologist is involved in several steps of diagnostics and treatment planning for patients with rectal tumors. Starting with the preoperative biopsy, the pathologist confirms the diagnosis of cancer and estimates the biological behavior of the tumor by classification and grading. Intraoperative diagnostics ensure the completeness of resection and postoperative examinations provide final histopathologicalandpTNM-classification.Additionally, information about the therapeutic response to neoadjuvant strategies is provided by the assessment of tumor regression. By including molecular pathological methods, the pathologist can evaluate predictive markers (e.g., KRAS mutation analysis for antibody therapy) and contribute to the diagnosis of hereditary nonpolyposis colorectal cancer (HNPCC) by analyzing microsatellite instability. This chapter describes the role of pathology in the management of rectal cancer.
3.2 Preoperative Biopsy Endoscopically visualized carcinomas must be confirmed by biopsy and histopathological examination in order to exclude lesions that may grossly resemble
T. Wiech (*) Institute of Pathology, Freiburg University Hospital, Breisacher Strasse 115a, 79106 Freiburg, Germany e-mail: [email protected]
carcinoma, such as solitary rectal ulcers due to prolapse. Rectal ulcers with reactive hyperplasia in the everted edge, which mimic adjacent adenoma, can be particularly difficult to distinguish macroscopically from ulcerating adenocarcinoma arising in an adenoma. Other differential diagnoses include scarring after diverticulitis. For a high level of diagnostic accuracy, at least five to six biopsies should be taken from the center and the margin of the lesion. If a biopsy is taken from the outer periphery, it will likely show noninvasive adenomatous characteristics. In contrast, if the biopsy is taken from the very center of the lesion, it may consist exclusively of necrotic tissue. Thus, several biopsies should be taken to ensure that enough malignant tissue is present to confirm the diagnosis (Fig. 3.1).
3.2.1 Histologic Classification Histopathologic classification is performed according to the World Health Organization Classification of Tumours (Hamilton et al. 2000). Rectal carcinoma is defined as a malignant epithelial tumor of the rectum that has invaded through the muscularis mucosae. In contrast, adenomas, representing precursor lesions of colorectal carcinoma, are noninvasive but show cellular dysplasia (i.e., intraepithelial neoplasia). Most adenomas have hyperchromatic and stratified spindleshaped nuclei with varying degrees of loss of polarity and cellular atypia (i.e., low-grade and high-grade intraepithelial neoplasia). The typical invasive adenocarcinoma, accounting for the vast majority of rectal cancer, consists of epithelial columnar
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