Risk of relapse and lack of benefit from adjuvant chemotherapy following surgical resection of early-stage appendiceal adenocarcinoma.

840 Background: There are no prospective studies evaluating the benefit of adjuvant chemotherapy (AC) for patients diagnosed with early-stage Appendiceal adenocarcinoma (AA). Current NCCN guidelines suggest that AA be treated the same as colon cancer, and that 5FU-based AC should be considered if CRC-derived “high-risk” features are present. Here we evaluate the benefit of AC and identify features associated with risk of relapse in the largest study of early-stage AA to date. Methods: Foundry software (Palantir, Denver, CO) was used to query the MD Anderson (MDA) EHR to identify and extract data from all patients all AA diagnosed between 2000 and 2024. Results: Among a total of 3,662 patients with AA, 439 (12.0%) were identified as early-stage. Interestingly goblet cell histology (GCA) was most common, 176 (40%), followed by mucinous 131 (30%), enteric 117 (27%), and signet ring cell (SRC) 15 (3%); this is a notable difference from metastatic patients where GCA account for only 12.8%. In 202 patients where surgery was performed at MDA only 19 (9.4%) relapsed. As expected, 5-yr relapse incidence was higher in stage 3 vs. 2 (30% vs 9.0%, HR 3.1). GCA had a particularly low 5-yr relapse (2%), relative to mucinous (14.5%), SRC (16.7%) and enteric (20%, p=0.006). In multivariate analysis of stage 2 tumors histologic subtype (HR 5.6 mucinous, 6.6 enteric, p