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Appendiceal tumors are uncommon, and their coexistence as collision tumors is exceedingly rare, with fewer than 20 cases reported to date. The objective is to report a multi-center case series and literature review of appendiceal collision tumors, providing a comprehensive summary of clinicopathological features and outcomes. Electronic records from five tertiary centers (2016-2024) were searched. Cases with appendiceal collision tumors composed of a neuroendocrine tumor (NET) and a second component of low- or high-grade appendiceal mucinous neoplasm (LAMN/HAMN) or adenocarcinoma were included. Additional cases with the same diagnostic combinations were identified through a PubMed literature search since 2000. Clinical, pathologic, and survival data were collected and analyzed. Thirty-three cases were identified, including 17 multi-institutional and 16 literature-derived cases, with an estimated incidence of 0.11% among appendectomies. Most tumors consisted of localized NET and LAMN. Gastrointestinal (GI) symptoms were present in 62.5-65.6% of cases, and tumors were identified by imaging in 53.1-75.0%. Outcome tracks the higher-stage and grade component. Patients with localized tumors had excellent outcomes (2-year progression-free survival [PFS] and overall survival [OS]: 100%). In contrast, cases with metastatic LAMN/HAMN had 2-year PFS 66.7% and OS 100%, while those with metastatic adenocarcinoma had 2-year PFS 0% and OS 66.7%. This study represents the largest series and literature review of appendiceal collision tumors to date. These rare tumors most often consist of localized NET and LAMN, typically present with GI symptoms, are often detected by imaging. The prognosis is dictated by the component of higher stage and grade.