Immunologic Fecal Occult Blood Testing Effective Screening Tool for Advanced Colorectal Cancer

Chicago—Fecal occult blood testing is routinely used to screen for colorectal cancer (CRC), and multiple methods are available. A team of Italian researchers assessed the effectiveness of immunologic fecal occult blood testing (FIT) at detecting advanced adenocarcinoma during initial and repeated screenings conducted biennially. A report of their findings, recognized as a poster of distinction at the DDW meeting, showed that FIT was most cost-effective during the first screening, with fewer persons needing to be screened to detect 1 case of advanced CRC than in the subsequent 3 screenings. In addition, the number needed to screen (NNS) to detect 1 case of neoplasm was higher for women than for men at every testing point. The researchers noted that the positive predictive value of follow-up colonoscopy for those patients who were FIT-positive remained relatively stable throughout the study. The poster was titled Screening for Colorectal Cancer by Immunological Fecal Occult Blood Test: Number Needed to Screen and to Scope to Find One Advanced Neoplasm. In October 2001, the researchers sent a letter to 2959 Italian residents 50 to 74 years of age inviting them to undergo CRC screening using FIT. Every 2 years over the next 6 years, consistent responders were invited to repeat the test. In the study’s first year, 2161 (73.3%) invited residents underwent screening with FIT, which returned positive results (>100 ng/mL) for 92 (4.2%) participants. All FIT-positive persons were referred for colonoscopy screening, which 87 ultimately received. Of those 87 individuals subjected to colonoscopy, 35 were found to have an advanced neoplasm. The authors calculated that 62 was the NNS with FIT to identify 1 case of advanced CRC and identified the number needed to scope (NNSC) as 2.5. In the second round of screening, 1559 (53%) of those tested previously underwent testing, and 67 (4.3%) of them were FIT-positive; 58 agreed to follow-up colonoscopy, which confirmed 18 cases of advanced neoplasm. The NNS increased to 87 and the NNSC rose to 3.2. A cumulative analysis of data from study inception through the second round produced an NNS of 173. A total of 971 participants (33%) agreed to a third FIT screening 2 years after the second one was performed. Only 33 (3.4%) of them were positive; 29 of those individuals received colonoscopy as recommended, which revealed 10 cases of advanced CRC. The NNS in the third round was 97 and the NNSC was 2.9. Cumulatively, from the start of the study, the NNS was 291. Only 713 (24%) of the original cohort received all 4 FIT screenings. The fourth round identified 36 (5.0%) FIT-positive patients, of which only 1 declined follow-up colonoscopy. In this round, 11 cases of CRC were confirmed, producing an NNS of 64 and an NNSC of 3.2. Looking at outcomes by sex showed that, during the first round of screening, FIT had to be administered to 89 women versus 45 men to detect 1 case of advanced CRC. In the colonoscopy subgroup, 3.8 women had to be scoped per a single CRC diagnosis compared with 2.3 men. The investigators said this “sharp difference” between men and women persisted throughout the study. Combining data from all 4 biennial tests produced an NNS of 259, which the authors said indicated a relatively stable trend in predictive value. “Over 4 rounds, 29 people had to be screened on average 2.6 times to detect 1 advanced neoplasm,” they concluded. The authors noted that a French study using guaiac fecal occult testing had reported a much higher NNS of 107, whereas the outcome of their study was relatively consistent with a prior study that produced an NNS with FIT of 41 per CRC diagnosis.