Time-related changes in the prognostic significance of the total number of examined lymph nodes in node-negative pancreatic head cancer

BACKGROUND AND OBJECTIVES: The aim of study was to assess time trends in the association between the total number of lymph nodes examined (TNLE) and survival in patients operated for adenocarcinoma of the head of pancreas. METHODS: Patients operated for node-negative adenocarcinoma of the head of pancreas between 1988 and 2007 were identified from the Surveillance, Epidemiology and End Results (SEER) database. Patients diagnosed between 1988 and 2002 were compared to those diagnosed between 2003 and 2007. RESULTS: A total of 3,406 patients were included. Although TNLE was associated with survival, the effect was not uniform. Compared to patients with >12 TNLE, survival decreased with lower TNLE (4-12 TNLE: hazard ratio [HR] 1.27, 95% CI 1.10-1.46; <4 TNLE: HR 1.39, 95% CI 1.20-1.60) among patients diagnosed between 1988 and 2002. In contrast, for those diagnosed between 2003 and 2007, while there was decreased survival for those with <4 nodes (HR 1.44, 95% CI 1.22-1.71), no effect was seen for patients with TNLE 4-12 (HR 0.98, 95% CI 0.85-1.14). CONCLUSION: The prognostic significance of the TNLE in patients operated for adenocarcinoma of the head of the pancreas is not constant over time.