Colorectal Advanced Adenomas: Frequency in Population At Risk and Correlation with the Quantitative Immunological Occult Blood Test

Abstract

Introduction: Colorectal cancer (CCR) is the most frequent digestive neoplasia; typically, more than 90% arise from an adenoma. Advanced Adenomas (AA) are lesions ≥10 mm, villous component ≥25% or high degree dysplasia with major risk of malignization. The Program of Prevention and Early Detection of CCR uses Immunological Faecal Occult Blood Test (IFOBT) as a screening to quantify haemoglobin of the faecal matter; those patients with levels ≥100 ng hb/ml were sent to colonoscopy. Our aims were to compare the frequency of AA in two groups: asymptomatic with IFOBT ≥100 ng hb/ml versus symptomatic. They were referred for colonoscopy. A second aim was to correlate of the size of the adenoma with the IFOBT. Methodology: We designed an observational study from of 2829 consecutive patient's sent to colonoscopy between April, 2000 and December, 2007 at the Digestive Cancer Center of the National Cancer Institute of Montevideo, Uruguay. Previous informed assent, we collected clinical, demographic information, presence of adenoma (size, topography and histology) and IFOBT quantification (ng hb/ml). Groups: 1) asymptomatic, >50 years old with IFOBT ≥100 ng hb/ml (n=1927), and 2) symptomatic (n=902). Statistical analysis was performed chi square, Student t-test, and multiple lineal correlations with SPSS 17.0 for Windows and Epi Info ver. 3.3.2.0. Results: The asymptomatic group (n=1927) were 81 (Females 31) AA from 902 (8.9%) IFOBT positive patients. Sixty five patients had only one AA (80.2%) and 16 two or more (19.8%). Size: ≤ 9 mm (n=22, 27,2%), 10-15 mm (n=51, 62.9%) and ≥16 mm (n=8, 9.9%). The quantification with IFOBT showed a positive correlation with the size of the adenoma. Interestingly, there was a point of inflexion at 15 mm size, where the IFOBT values stop increasing (flat curve) at the interval between 1100 and 1900 ng Hb. For every mm that increases the size, the IFOBT increased 35 ± 9 ng Hb. The symptomatic group had 105 AA out of 1927 (5.1%) symptomatic patients. No differences were observed by age, sex or place of the lesions. Conclusions: The comparison between those two different groups at risk allows detecting incipient lesions asymptomatic patients. The use of the IFOBT as a screening tool for colonoscopy detected a major frequency of advanced adenomas in asymptomatic patients that in symptomatic. In patients with average risk for colorectal cancer the IFOBT is a useful tool for screening; colonoscopy in patients with positive test showed that the size of the adenoma is in directly relation with the level of the microhemorrhage.