The annual incidence of colon cancer in the United States is about 55 cases per
ID: 96903 • Letter: T
Question
The annual incidence of colon cancer in the United States is about 55 cases per 100,000. Because colon cancer often causes bleeding, doctors sometimes use a screening procedure called the fecal occult blood test (FOBT) to look for tiny amounts of blood in the feces. One form of this test has a specificity of about 98%, which means that when it indicates the presence of blood in the feces, the result is an error (i.e., cancer is not present) only 2% of the time. While this may seem like excellent specificity, a 2% "false positive" rate makes this test almost useless as a tool for colon cancer screening.
Why is this test almost useless as a tool for colon cancer screening?
a) FOBT determines colon cancer that should be immediately excised, but a 2% false positive rate means that some healthy patients would undergo surgery. b) The 2% false positive rate is much higher than other techniques so this procedure is useless, even though this is excellent specificity. c) Testing 100,000 people, the 2% false positive rate yields many more incorrect results (55) compared to real cancer cases (2,000). d) Testing 100,000 people, the 2% false positive rate yields many more incorrect results (2,000) compared to real cancer cases (55).Explanation / Answer
FOBT is a type of screening test that could indicate colorectal cancer,but not diagnose it.This test checks for blood in the stool,and if blood is detected additional testing is required to determine the source of blood.FOBT is never used to diagnose colon cancer,if blood is detected in the stool then other tests like colonoscopy,flexible sigmoidoscopy or a virtual colonoscopy should be done.
FOBT is a useless tool for this screening because testing 100,000 people,the 2 % false positive rate yields 2000 incorrected result as compared to 55 real cancer cases
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