EPID-27. THE INCIDENCE OF BRAIN METASTASIS IN GASTROINTESTINAL CANCER ACCORDING TO PRIMARY SITE AND STAGE: A 15-YEAR SINGLE INSTITUTIONAL ANALYSIS

Abstract Gastrointestinal (GI) cancers are a diverse group of cancers including pancreatic, gastric/gastroesophageal junction/esophageal (G/GEJ/E), colorectal (CRC), hepatocellular (HCC), biliary tract (BT), and anal origin cancers. The risk of developing brain metastasis (BrM) is not well characterized. The aim was to determine the incidence of BrM among all GI cancer patients at Princess Margaret Hospital (PM). We included patients diagnosed with GI cancer presenting from 2005-2020, captured prospectively in our institutional registry. These patients were cross-referenced with our radiotherapy database, where radiotherapy for brain metastases (BrM) was used as a proxy for the brain metastases development. Cumulative incidences (CI) of BrM diagnoses were calculated using death as a competing risk. Overall survival (OS) was estimated using the Kaplan Meier method. The registry accounted for 22,188 patients. The median age of the cohort was 64. Most common primary sites are CRC adenocarcinoma, pancreatic adenocarcinoma, G/GEJ/E adenocarcinoma were 31.52%/11.71%/10.25%. The 15-year CI for BrM for the entire cohort was 1.65%, and for CRC, small bowel, anal, pancreatic, G/GEJ/E, HCC, and BT cancers were 2.69%/2.49%/1.30%/0.5%/3.52%/ 0.05% /0.4% (p < 0.001) and Stage I-IV disease were 0.39%/0.81%/1.2%/3.1%, respectively (p < 0.001). 5 year CI for HER2 positive G/GEJ/E patients was 19.5%. Median OS from initial presentation for those with BrM was 25.13 months. On univariable analysis, chemotherapy receipt [HR 1.916, p < 0.001], Stage IV at presentation [HR 3.991, p < 0.001], and G/GEJ/E primary [HR 1.357, p < 0.001] predicted for higher risk of BrM. Multivariable analysis confirmed that receipt of chemotherapy and Stage IV disease predicted a higher risk for BrM and pancreatic, HCC, and BT cancers predicted for lower BrM. We observed that among patients diagnosed with GI cancers, Stage IV disease predicted higher risk for developing BrM and were more likely to receive chemotherapy.