Characteristics and outcomes of patients with early-onset versus average-onset small bowel neuroendocrine tumors.

670 Background: The global incidence of early-onset gastrointestinal cancers (GI) is increasing. Although patients with more common early-onset GI cancers, e.g. colorectal cancer, often present with more advanced disease and experience relatively worse outcomes; the characteristics and treatment outcomes for less common early-onset small bowel neuroendocrine tumors (SBNETs) have yet to be explored. Methods: We used the Surveillance, Epidemiology, and End Results (SEER) database to identify patients with SBNETs (2004-2021), using ICD-0-3 SEER histology codes (8240/3, 8241/3, 8243/3, 8244/3, 8249/3, 8246/3). Patients with poorly differentiated histology were excluded. We used the chi-square test to compare categorical variables between early-onset SBNETs (EO-SBNETs, aged 30-49 years) and average-onset SBNETs (AO-SBNETs, aged ≥ 50 years) patients. Overall survival was estimated using the Kaplan-Meier method followed by application of the log-rank test to assess for differences in survival. A multivariable Cox regression analysis included early onset of disease, sex, race/ethnicity, marital status, urban/rural residence, prior treatments, and disease extent as covariates. All tests were conducted with a significance threshold of p < 0.05 using RStudio. Results: A total of 3,713 patients were included, of which, 925 (25%) were EO-SBNETs. Compared to AO-SBNETs, EO-SBNETs patients were more likely to be females (51.1% vs 46.7%, p=0.02), non-Hispanic Black (20.8% vs 17.6%, p=0.04), Hispanic (13.6% vs 8.8%, p<0.0001) and less likely to be non-Hispanic White 60.8% vs 69.9%, p<0.0001). There were no differences in stage at diagnosis between the EO-SBNETs and AO-SBNETs, i.e,, localized disease (33.5% vs 31.0%, p=0.15), regional spread (41.9% vs 42.8%, p=0.64) and distant metastatic disease (20.9% vs 21.9%, p=0.50). There were no differences in receipt of surgical resection (90.5% vs 89.1%, p=0.25) or chemotherapy (5% vs 6.3%, p=0.15) comparing EO-SBNETs and AO-SBNETs respectively. In a multivariate cox regression analysis, early onset was associated with a significantly better overall survival (HR=0.49, 95% CI 0.41-0.59, p<0.0001). Conclusions: With this first of its kind analysis, significantly superior overall outcomes among EO-SBNETs despite no differences in stage and receipt of surgery establishes age at diagnosis as a significant prognostic factor for SBNETs. Further studies investigating the role of factors such as differences in tumor biology and patient preferences in receipt of other therapies besides surgery are needed.