Colorectal cancer (CRC) is a malignant epithelial neoplasm (adenocarcinoma) developing in the glandular tissue of the colon or rectum. The great majority of CRCs develop from adenomatous colorectal polyps in a process called the adenoma-carcinoma sequence (Muto et al., Cancer 36(6):2251–2270, 1975). Colorectal polyps are a histopathologic group of benign lesions that include hyperplastic and adenomatous polyps that project above the surrounding mucosa as well as the less common, non-polypoid polyps. The adenomatous polyps (adenomas) are benign, neoplastic precursors that arise in the colorectal glandular epithelium. In the United States (USA), colorectal adenoma (CRA) prevalence is approximately 25 % by age 50 and rises to around 50 % by age 70. The histological hallmarks of a CRA are altered glandular architecture and dysplasia of the epithelium. A benign CRA progresses to invasive CRC when the dysplastic cells gain the capacity to invade through the muscularis mucosa. The development of invasive cancer from the earliest CRA may take from years to decades. While most CRCs develop from CRAs, the slow rate of progress results in less than 10 % ever progressing to CRC. In this chapter, we review the molecular characteristics of the disease and provide an update on the epidemiology including reviewing evidence for established and suspected risk factors for CRC. Given the dramatic impact that screening and early detection have had on reducing the incidence and mortality suspected of CRC and death from CRC, we have included a detailed review of the different screening recommendations and their efficacy.
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