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Adapted from the NCI Cancer Bulletin, vol. 4/no. 26, Sept. 25, 2007 (see the current issue).
In a large prospective study performed by investigators from three Northern California Kaiser Permanente medical centers, a type of fecal occult blood test (FOBT) called a fecal immunochemical test (FIT) showed high sensitivity and specificity for detecting left-sided colorectal cancer. The results were published online on September 25, 2007, by the Journal of the National Cancer Institute (see the journal abstract).
The investigators enrolled 7,394 eligible Kaiser Foundation Health Plan members aged 50 or older without a personal or family history of colon cancer into the study. All participants collected stool samples for use on three test cards, and the samples on each test card were used for three tests: a sensitive unrehydrated guaiac test (GT, a more sensitive version of the current standard FOBT), the FIT, and a combination of those two tests. Out of all participants, 5,841 prepared cards correctly and had at least one usable test result. Of these, 11 percent had at least one positive result.
Investigators recommended that all participants testing positive on the FIT or combination tests undergo colonoscopy, and all participants testing negative undergo sigmoidoscopy. Because most participants tested negative and underwent sigmoidoscopy, which can only visualize the left colon, only detection of left-sided colorectal cancer could be compared between tests. All participants were followed for two years, until diagnosis of a colorectal neoplasm, or until death, whichever came first.
The FIT had an 81.8 percent sensitivity for detecting colorectal carcinoma, and a 29.5 percent sensitivity for detecting advanced colorectal adenomas (noncancerous tumors). Specificity was 96.9 percent for carcinomas and 97.3 percent for adenomas, which increased to 98.1 percent and 98.4 percent in the combination test.
Although the investigators did not directly compare the FIT test with the current standard FOBT test, other recent comparisons have shown its superiority, they explain. "The FIT has high sensitivity and specificity for detecting left-sided colorectal cancer," they conclude, "and it may be a useful replacement for the [current standard test]."
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