Mo1192 Impact of Incidental Findings of 18 FDG-PET/CT in the Patients With Gastric Cancer

Abstract

Background The NHS Bowel Cancer Screening Programme (BCSP) in England has used the guaiac-based faecal occult blood test (gFOBt) since 2006. The kits have six windows (three pairs) lined with guaiac-impregnated filter paper to which two faecal samples from three consecutive stools are applied. The samples usually arrive dry at the laboratory, which is likely to reduce the degree of haemoglobin (Hb) degradation and provide the best opportunity to detect bleeding. The amount of bleeding from bowel cancer lesions and adenomas is directly related to the degree of bowel pathology. BCSP policy is that every kit is logged on the day of receipt and read as soon as possible thereafter. Test positivity is higher during the first 5 days after sample collection, but the reasons for this are unclear. Vegetable peroxidases in the diet and their rapid degradation in faeces is one possible explanation. Method BCSP Southern Hub data from the Bowel Cancer Screening System for 01/200807/2012 were analysed for subjects aged 60-69 years completing the first prevalent round of screening. The interval between each sample date and the date the sample was analysed (elapsed time) was calculated. Spot positivity was assessed by elapsed time, stratified by sex. Clinical outcomes were extracted from BCSS for subjects who had a positive gFOBt result. The relationship between positivity, elapsed time and clinical outcomes was examined. Results Overall, 92% of test kits were read in the Hub within 5 days of the last sample collection. For samples analysed one day after the last sample collection, spot positivity was 2.7% for women and 3.8% for men. Positivity declined thereafter until it reached a steady level at day 5 (women 1.3%; men 2.0%). Positivity for the most recently collected sample (spots 5 and 6) was slightly higher than for the spots collected earlier. There were 20,408 subjects (8,343 women; 12,065 men) referred for further investigation after gFOBt testing during the study period. The outcome of those further investigations was not associated with elapsed time between faecal sampling and test kit reading; the proportion of cancers, high-, intermediate and low-risk adenomas was fairly constant as elapsed time increased. Conclusions The higher positivity associated with a shorter elapsed time is not associated with a higher proportion of false-positive tests. There is the possibility that the fairly constant yield of false and true positives over time could reflect a balance between vegetable peroxidase degradation and the degradation of Hb associated with various degrees of pathology. Conversely, the higher positivity during the first few days after sample collection might be explained simply by the possibility that worried (perhaps symptomatic) individuals may return the test kit for analysis more quickly. Further work is required to confirm these observations.