Luminary Learning Gastrointestinal Disorder- Issue 1

30  • LUMINARY LEARNING: GASTROINTESTINAL DISORDERS zz Development of sporadic colorectal cancer is a slow process that takes 7–10 years to progress through a number of genetic steps from normal mucosa through precursor lesions (polyps) to an invasive and metastasizing cancer. This long interval provides us with an opportunity to intervene by screening for and eliminate precancerous lesions. zz Diagnostic colonoscopy is done as part of a workup for specific symptoms such as a positive fecal occult blood test, chronic anemia, or gross rectal bleeding. zz Screening programs aim at reducing the incidence of CRC by removing precursor lesions and to improve cancer survival by detecting cancer at an earlier stage Introduction Colorectal cancer (CRC) is the most common malignancy in the gastrointestinal tract. Over a life- time, it affects 1 in 22 individuals (4.5%) of the general population in Western civilizations includ- ing the United States. Worldwide, however, there is a much larger geographical variation, with a crude incidence of 6.5/7.7 cases per 100,000 females/males in less developed areas as opposed to 48.3/36.6 in more developed regions. Since the mid-1980s, there has been a steady decrease in overall incidence in the United States, whereby some subgroups such as patients younger than 50 or African-American males in fact showed an increase or remained unchanged. According to the American Cancer Society despite the overall decline in incidence and mortality, CRC remains the third most frequently diagnosed cancer in both the U.S. men (lung/prostate) and women (breast/ lung) and accounts for the third most common fraction of cancer death (behind lung, prostate/ breast) [1]. In gender-neutral absolute numbers, colorectal cancer ranks fourth in annual cancer incidence (behind breast, lung, and prostate, respectively, excluding skin cancers) and second in cancer mortality (behind lung cancer) [1]. An estimate for 2016 of the incidence in the United States projects 95,270 new colon cancer and 39,220 new rectal cancer cases (total 134,490 cases); furthermore, 49,190 people are anticipated to succumb to colorectal cancer in 2016 [1]. The majorities of CRC cases are sporadic cancers and typically arise within a polyp. Adenomatous and serrated polyps are two subtypes that possess the potential to transform into a cancer through a series of gene mutations (“adenoma-carcinoma sequence”). The prevalence of polyps is an age-dependent phenomenon that increases from 11% at age 40–49 to 15% at age 50–59 [2]. In fact, up to 45–50% of asymptomatic average-risk individuals who undergo screen- ing are found to have at least one polyp, of which about half shows an adenomatous (90–95%) or serrated (5–10%) pathology. This epidemiology translates into an estimated cancer risk of 1 in 5 polyps ultimately transforming into a cancer. Moreover, early detection is key as cancer-specific survival at 5 years is 65% for all tumor stages together, but it is directly correlated to the tumor stage with 90% for local (stages I/II), 71% for loco-regional (stage III), and 13% for distant meta- static disease (stage IV), respectively [1, 3]. Concept of CRC Screening and Surveillance vs. DiagnosticWorkup Since clinical symptoms are almost always late signs of colorectal cancer and hence not relia- ble for early risk or disease detection and since earlier tumor stages are associated with better