Mismatch repair–deficient tumors do not respond well to chemotherapy applied in the neoadjuvant, adjuvant, or metastatic settings. Mismatch repair deficiency occurs in 5% to 10% of patients with rectal adenocarcinomas. A major pooled analysis evaluating the impact of T and N stage and treatment on survival and relapse in patients with rectal cancer who are treated with adjuvant therapy confirmed these findings. Only disease stage (designated by tumor, nodal status, and distant metastasis ) has been validated as a prognostic factor in multi-institutional prospective studies. Presence of MSI that results from impaired DNA mismatch repair.Measured in millimeters, CRM is defined as the retroperitoneal or peritoneal adventitial soft-tissue margin closest to the deepest penetration of the tumor. Circumferential resection margin (CRM) or depth of penetration of the tumor through the bowel wall.Other risk factors for colorectal cancer include the following: Increasing age is the most important risk factor for most cancers. The bony constraints of the pelvis limit surgical access to the rectum, which results in a lower likelihood of attaining widely negative margins and a higher risk of local recurrence. The distance of the tumor from the anal sphincter musculature has implications for the ability to perform sphincter-sparing surgery. The location of a rectal tumor is usually indicated by the distance between the anal verge, dentate line, or anorectal ring and the lower edge of the tumor, with measurements differing depending on the use of a rigid or flexible endoscope or digital examination. By rigid sigmoidoscopy, the rectum measures between 10 cm and 15 cm from the anal verge. The rectum is located within the pelvis, extending from the transitional mucosa of the anal dentate line to the sigmoid colon at the peritoneal reflection. AnatomyĮnlarge Anatomy of the lower gastrointestinal (digestive) system. Among all racial groups in the United States, Black individuals have the highest sporadic colorectal cancer incidence and mortality rates. Deaths: 52,580 (rectal and colon cancers combined).Ĭolorectal cancer affects men and women almost equally.
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