BACKGROUND: Although positive peritoneal lavage cytology has been established as an important prognostic factor in gastric and pancreatic cancers, its significance in duodenal cancer remains unclear. METHODS: This study analyzed 74 consecutive patients with peritoneal lavage cytology who underwent surgical resection for duodenal cancer at our institution between 2002 and 2020. (pancreatoduodenectomy, n = 58
partial resection, n = 11
and pancreas-sparing total duodenectomy, n = 5). Clinicopathologic features and survival outcomes were analyzed, focusing on the peritoneal lavage cytology status. RESULTS: Among the 8 peritoneal lavage cytology -positive patients, the primary tumor depth was classified as pT3 in 1 case and pT4 in 7 cases. The recurrence-free survival and overall survival rates were markedly worse in peritoneal lavage cytology-positive patients than in peritoneal lavage cytology-negative patients (5-year recurrence-free survival: 0.0% vs 78.0%, P <
.001
5-year overall survival: 12.5% vs 82.4%, P <
.001). In a subgroup analysis of patients with T3 or T4 tumors (n = 38), the recurrence-free survival and overall survival were significantly poorer in patients with peritoneal lavage cytology-positive tumors than in those with peritoneal lavage cytology-negative tumors (5-year recurrence-free survival, 0.0% vs 51.8%, P = .001
5-year overall survival, 12.5% vs 60.9%, P = .005). A multivariate analysis identified a peritoneal lavage cytology-positive status as an independent prognostic factor for the overall survival (hazard ratio, 3.38
P = .023). CONCLUSION: Peritoneal lavage cytology positivity in patients with duodenal cancer was associated with advanced tumor progression and was a significant prognostic marker. This finding underscores the importance of peritoneal lavage cytology as a valuable tool for identifying patients who may require multidisciplinary treatment approaches.