Introduction: Appendiceal adenocarcinoma represents a diagnostic and therapeutic challenge since it is prone to early lymphatic and peritoneal spread. We aimed to analyze the proportion of lymph node metastases in completion right hemicolectomy specimens, risk factors for peritoneal metastases (PM), and prognosis after definitive treatment.

Methods: Ninety-three patients with appendiceal adenocarcinoma scheduled for cytoreductive surgery and hyperthermic intraperitoneal chemotherapy (CRS + HIPEC) in Uppsala 2004-2020 were identified from a prospectively maintained registry. Risk factors for PM were assessed based on the presence (CT + group, n = 55) or absence (CT - group, n = 37) of visible PM at baseline CT scan. Prognostic factors were analyzed based on the actual presence (PM group, n = 66) or absence (no PM group, n = 27) of PM.

Results: The median age was 60 (26-78). Forty-eight patients were women. Resection of PM at initial surgery indicated an 80 % risk of finding PM at a follow-up exploration. R1 appendectomy and perforated appendix had a similar risk for PM (24 %,26 %) which increased to 38 % if both were present. Regional lymph node metastases occurred in 31 % in the CT + group vs. 14 % in the CT- group (p = 0.005) and was associated with poor survival HR 5.16 (1.49-17.81). The 5-year OS and DFS rates were 54 % and 29 % in the PM group.

Conclusions: Patients with certain risk factors have a high likelihood of PM despite a normal CT scan, which justifies selective exploration at a HIPEC center. Regional lymph node spread supports the current practice of completion right hemicolectomy and is a significant prognostic factor.