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Gastrointestinal Oncology - part 5

Bệnh nhân phát triển u tuyến có nguy cơ suốt đời gia tăng phát triển ung thư đại trực tràng. • Loại bỏ các khối u giảm tỷ lệ mắc bệnh ung thư. Bệnh nhân bị u tuyến nhỏ có nguy cơ 2.3-gia tăng của bệnh ung thư sau khi cắt polyp | 162 Chapter 10 Colonic adenomas occur more frequently in patients who have colorectal cancer. Nearly a third of all patients with colorectal cancer will also have a benign colorectal polyp. Patients who develop adenomas have an increased lifetime risk of developing colorectal cancer. Removal of polyps decreases the incidence of cancer. Patients with small adenomas have a 2.3-increased risk of cancer after the polyp is removed compared with an 8-fold increased incidence of colorectal cancer in patients with polyps who do not undergo polypectomy. Populations with a high risk of colorectal cancer also have a high prevalence of colorectal polyps. Patients with familial adenomatous polyposis will develop colorectal cancer virtually 100 of the time in the absence of surgical intervention. The adenomas that characterize this syndrome are genetically identical to sporadic adenomas. The peak incidence for the discovery of benign colorectal polyps is 50 years of age. The peak incidence for the development of colorectal cancer is 60 years of age. This suggests a 10-year time span for the progression of an adenomatous polyp to a cancer.4 These observations and studies by molecular biologists document that colonic mucosa progresses through stages to the eventual development of an invasive cancer. Colonic epithelial cells lose epithelial homeostasis the balance between proliferation and apoptosis or programmed cell death that produces normal regeneration. With more proliferation and increasing cellular disorganization the cells extend through the muscularis mucosae to become invasive carcinoma. The process of colorectal carcinogenesis generally follows the predictable sequence of invasion of the muscularis mucosa pericolic tissue lymph nodes and finally distant metastasis. Sporadic Colorectal Cancer It is important to recognize the increased risk of cancer in patients with hereditary cancer syndromes but by far the most common form of colorectal cancer is sporadic in nature .