Study of In-home Tests for Colorectal Cancer

Overview

The objective of this study is to compare the performance characteristics or accuracy of different in-home screening tests for colorectal cancer (fecal occult blood tests), among patients without symptoms of colorectal cancer. Patients who meet study eligibility criteria and agree to participate in the study are asked to perform one guaiac and two immunochemical fecal occult blood tests at home prior to their colonoscopy. After the patient has completed and sent in the test kits, the patient then undergoes their previously scheduled colonoscopy. Accuracy and performance characteristics for each type of fecal occult blood test, including sensitivity, specificity, test positivity rate and positive predictive value for advanced colorectal neoplasia (advanced colorectal polyps) or colorectal cancer, will be estimated by comparing the fecal occult blood test results with the results of the colonoscopy.

One of the recommended options for colorectal cancer screening in the population at average risk for colorectal cancer is annual fecal occult blood test (FOBT) starting at age 50. Randomized controlled trials have shown that annual or biennial fecal occult blood testing using a guaiac-based test reduces incidence and mortality from colorectal cancer. However, the sensitivity and specificity of the guaiac-based tests is relatively low. Guaiac-based fecal tests can produce false-positive or false-negative results with certain foods, vitamins, or medications, so dietary restrictions are generally recommended before the test. Newer, immunochemical FOBTs use antibodies to detect the globin portion of human hemoglobin and do not require dietary restrictions. These immunochemical tests may have improved performance characteristics (sensitivity and specificity) compared with the guaiac-based tests. However, there have been few studies of the performance characteristics of the immunochemical tests in the average-risk population, particularly for the iFOBTs that are currently available in the U.S. There are several iFOBT tests on the U.S. market which may have different performance characteristics. Some of the newer immunochemical tests also have the advantage of having a simpler sampling procedure for the patient. Guaiac-based FOBTs generally use sticks or spatulas to collect specimens from three stools that have not contacted toilet bowl water; these specimens are then smeared on test cards. However, some immunochemical tests allow sample collection by brushing the surface of the stool while it is in the toilet bowl water. In addition, some immunochemical tests only require samples from one or two stools. Colorectal cancer is a leading cause of cancer-related morbidity and mortality. Key policy groups including the ACS, the American College of Radiology, the U.S. Multi-society Task Force on Colorectal Cancer, and the U.S. Preventive Services Task Force recommend the FOBT (guaiac or immunochemical-based) as one of several appropriate screening strategies for colorectal cancer. Although colonoscopy has higher sensitivity and specificity than FOBT in detecting advanced colorectal neoplasia, colonoscopy is an invasive test that has several potential disadvantages when screening the average-risk population, including higher costs, capacity limitations, and increased risk of complications. Immunochemical FOBT may have some advantages over both guaiac-based FOBT and colonoscopy for screening the average-risk population, including better performance characteristics and better patient acceptability than gFOBT and lower costs than colonoscopy. Unfortunately, the scientific literature on the sensitivity and specificity of the respective tests is not sufficient to support more specific recommendations about which test is best for routine screening among asymptomatic adults. This study will address that crucial gap in the literature.