Although screening programmes allow to physicians detect colorectal cancer disease when it is in its initial stages, there are a small group of patients who suffer the consequences of a 'false positive.' This means that the blood found in the stool may be due to benign pathologies such as (haemorrhoids or polyps) and not from cancer and, therefore, a colonoscopy should be performed to confirm the diagnosis. Reducing the possibility of a 'false positive' result is very important to improve the risk-benefit balance of screening programmes.
Most colorectal cancers develop from lesions called adenomatous polyps, precancerous lesions. Both polyps and cancers bleed intermittently, and it is this blood that can be detected through the test offered by the Early Detection Program. Colorectal cancer can develop for months without causing discomfort and often, when it appears, the disease is already quite advanced. Early detection programs make it possible to detect the disease in its early stages, which makes it easier to treat and increase the chances of cure. This is probably one of the best examples of how early detection improves the prognosis of the disease and reduces the aggressiveness of the treatments.
Researchers from the Oncology Data Analytics Program (PADO) and the Screening Unit of the Cancer Prevention and Control Program of ICO and CIBERESP, coordinated by the ICO-IDIBELL researcher, Víctor Moreno, have published a study to estimate the cumulative risk of a 'false positive' result in the faecal occult blood test during seven rounds of colorectal screening performed in the area of influence of the ICO and identified its associated factors in a population-based colorectal cancer screening program.
The study, ‘False-Positive Results in a Population-Based Colorectal Screening Program: Cumulative Risk from 2000 to 2017 with Biennial Screening’, published in Cancer Epidemiology Biomarkers & Prevention, reported that the accumulated risk of a 'false positive' result was 16.2% adjusted for age, sex and type of test. These data indicate that participants who begin screening at the age of 50 and complete the ten rounds of screening until the age of 69, have more than 20% chance of having a 'false positive.' Anyway, the only harm would be having to do an unnecessary colonoscopy.
"We believe that the cumulative risk of a 'false positive' in colorectal screening using a faecal occult blood test seems acceptable, since colonoscopy lengthens the time required to perform another additional colorectal screening, while rates of complications remain relatively low," concluded the article's corresponding author and responsible for the research at the Screening Unit of the Catalan Institute of Oncology, Dr Montserrat García.