Histopathological yield of completion right hemicolectomy in appendiceal mucinous neoplasms: a single-centre retrospective cohort study

The role of right hemicolectomy (RHC) in low-grade and high-grade appendiceal mucinous neoplasms (LAMN and HAMN) has progressively diminished as their predominantly peritoneal rather than lymphatic pattern of dissemination has become better recognized. However, the actual histopathological yield of completion RHC performed after previous appendectomy remains poorly characterized. This study evaluated the histopathological findings of completion RHC in a historical, predominantly LAMN cohort. This retrospective single-centre cohort study included patients with LAMN or HAMN treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy between 2017 and 2026. Patients with invasive appendiceal adenocarcinoma were excluded. Completion RHC was defined as right hemicolectomy performed after previous appendectomy. Histopathological findings were classified as absence of both mucinous neoplastic epithelium and acellular mucin, acellular mucin only, or cellular mucinous neoplastic disease. Regional lymph-node involvement and resection-margin status were also assessed. In an exploratory analysis, Peritoneal Cancer Index (PCI) was compared according to the presence of cellular neoplastic disease in the colectomy specimen using the two-sided Mann–Whitney U test. The final cohort comprised 50 patients, of whom 22 underwent completion RHC. Histopathology reports were evaluable in 20 cases. Twelve specimens (60.0%) contained neither mucinous neoplastic epithelium nor acellular mucin, while 4 (20.0%) contained acellular mucin only. Cellular mucinous neoplastic disease was identified in 4 specimens (20.0%); thus, 16 of 20 completion RHC specimens (80.0%) contained no mucinous neoplastic epithelium. A total of 317 regional lymph nodes were examined (median 15 per patient, IQR 13–17.5). No nodal metastases were identified in 20 patients (0%; exact 95% CI 0–16.8%). Patients with cellular neoplastic disease in the colectomy specimen had a higher median PCI than those without cellular disease (14.0 [IQR 10.3–17.3] vs. 4.5 [IQR 3.0–8.3], p = 0.016). Completion RHC identified cellular mucinous neoplastic disease in 20% of evaluable specimens, while no regional lymph-node metastases were observed. When considered alongside existing evidence, these findings support selective use of completion RHC in LAMN and argue against its routine use solely for regional lymph-node clearance. Bowel resection remains appropriate when required for direct local involvement or complete cytoreduction.