Uri Ladabaum Stanford University School of Medicine, Stanford, CA, USA The images in this chapter illustrate key concepts related to the natural history of colorectal cancer in an average‐risk population as well as colorectal cancer screening and surveillance in average‐risk and higher‐risk persons (Figures 37.1–37.12). They also illustrate the spectrum of colorectal neoplasia that is encountered in the course of colorectal cancer screening and surveillance. Figure 37.1 Guaiac‐based fecal occult blood tests (gFOBTs) and fecal immunochemical tests (FITs) are used to screen stool for occult blood that could signal the presence of colorectal neoplasia. (a) Wooden sticks are used to apply smears of stool on gFOBT test card windows (left), which are then developed using a peroxide‐containing developer (small bottle, left) and read by looking for color change. Some FITs use brushes or sticks to collect stool into vials (right). (b) FITs that can be processed by machines with high throughput are favored for population‐based screening. Figure 37.2 Schematic of the natural history of colorectal cancer (CRC) in an average‐risk population, and the possible consequences of screening. (a) Without screening, 5–6% of persons develop colorectal cancer (light and dark blue) and 2–3% die from colorectal cancer (dark green). (b) Screening persons with adenomas that would develop into colorectal cancer may result in cancer prevention through polypectomy (Screen 1) or early cancer detection (Screen 2), both of which may result in prevention of colorectal cancer death. (c) Screening persons with adenomas that would not have developed into colorectal cancer may result in polypectomy, but no impact on colorectal cancer incidence or mortality. (d) Screening persons with a normal colon yields no colorectal‐related benefit. The population‐wide benefits of screening must outweigh the risks. Figure 37.3 In persons found to have colorectal neoplasia at screening colonoscopy, the most common findings are one or two small adenomas. Seen here are one small adenoma on the near fold on the left and a second adenoma on a superior fold more proximally in the colon (farther away in the image). Although it is logical to assume that larger and advanced adenomas were once small adenomas, the natural history of small adenomas is not well known. Surveillance guidelines in the USA have evolved towards longer intervals after removal of 1–2 small adenomas. Currently, surveillance at 7–10 years is recommended. European guidelines identify patients with 1–2 small adenomas as low risk, and recommend returning to regular screening.
CHAPTER 37
Colorectal cancer screening
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