BN SO24 - Predicting incidental gallbladder cancer: A protocol for identifying predictive factors of incidentally detected gallbladder cancer and prospective validation of a scoring system to allow selective histological analysis of the gallbladder

Abstract Background Incidental Gallbladder Cancer (iGBC) is a rare complication of cholecystectomy, with a UK incidence of 0.14-0.3%. Despite its rarity, most gallbladder specimens are analysed histologically. Some comparable countries undertake Selective Histological Analysis (SHA), selecting high-risk specimens for histology based on clinical judgement or postoperative inspection. However, evidence suggests a third of diagnoses can be missed with these approaches. Swedish and Dutch diagnostic scores incorporate few risk factors and are not generalisable to the UK. We present a protocol for a UK study aiming to develop a detailed diagnostic score for iGBC to reliably stratify patients by their risk of iGBC. Method This UK multicentre, cross-sectional, trainee-led study includes adult patients undergoing cholecystectomy for benign indications. It incorporates a feasibility study and an adaptive design, and has been submitted for ethical review. A parallel qualitative study will explore attitudes towards the risk of iGBC and the acceptability of SHA among patients and healthcare professionals. The feasibility phase will include 500 patients over six months, collecting data on patient risk factors for iGBC, preoperative investigations, operative findings, and histology results. Exclusion criteria include cholecystectomy as a secondary procedure, polyps over 5mm, and conditions known to increase the risk of biliary tract cancers. Results Following the feasibility phase, the recruitment rate and data completeness will be evaluated. Outcomes will be assessed against anticipated values, and collaborators will be surveyed to identify challenges with data collection. Necessary adjustments to the electronic case record form or overall protocol will be made, and the recruitment target will be recalculated based on an updated sample size calculation. When the study meets specified progression criteria, additional sites will be recruited, and data collection will continue to meet the required sample size. A detailed statistical analysis plan will be provided at a later date. Conclusion This protocol describes a UK diagnostic modelling study aimed at developing a risk-stratification score for iGBC in patients undergoing routine cholecystectomy, identifying high-risk patients and facilitating SHA.