Abstract
BACKGROUND AND PURPOSE: Small intestinal adenocarcinoma (SIA) is a rare cancer with a poor prognosis. Optimal treatment strategies are unclear as biological understanding of the disease is limited and randomized controlled trials are lacking. Current management is based on protocols for other gastrointestinal cancers. Therefore, the AdenoCarcinoma of the Small Intestine (ACSI) cohort was initiated, a subcohort of the nationwide Prospective Dutch ColoRectal Cancer cohort (PLCRC) study. The ACSI cohort aims to provide a large-scale, prospective SIA cohort, where clinical and molecular data will be combined to improve knowledge on tumor biology, treatment responsiveness, disease outcome and patient reported outcomes (PROs). Patient/material and methods: All adult SIA patients in the Netherlands are eligible for inclusion. Nationwide inclusion is facilitated by 68 hospitals. Clinical data are collected, as well as optional PROs, pathology- and blood samples. RESULTS: Until June 2025, 143 patients have been enrolled. Data of the first 105 patients show a median age of 65 years (interquartile range 58-73) at diagnosis with a slight male predominance (60%). Most tumors are located in the duodenum (57%) and 27% of patients present with stage IV disease, with a majority having single-site metastases (64%). Primary tumor resection is performed in 80%, while systemic treatment is administered in 42%. Four patients did not receive any anti-tumor treatment (14%). Mismatch repair deficiency is detected in 28% of patients. INTERPRETATION: The ACSI cohort enables structured national collection of clinical data, tumor samples and PROs of SIA patients. These data provide a valuable source for further research and improvement of care for this patient group.