Association Between Very Small Tumor Size and Decreased Overall Survival in Node-Positive Pancreatic Cancer

Abstract

Background: In pancreatic adenocarcinoma (PDAC), increasing tumor size usually correlates with a worse prognosis. However, patients with a very small primary tumor who experience lymph node involvement may have a different disease biology. This study sought to determine the interaction between tumor size and lymph node involvement in terms of overall survival (OS). Methods: The study identified 17,073 patients with a diagnosis of M0 resected PDAC between 1983 and 2013 using the Surveillance, Epidemiology, and End Results database. The patients were stratified by lymph node involvement (N0 vs N+) and T stage (T1a–T1b vs T1c vs T2 vs T3 vs T4). The Kaplan–Meier method was used to estimate OS, and Cox regression analysis was used to compare survival between subgroups after adjustment for patient-specific factors. Results: Lymph node involvement and T stage significantly interacted (p < 0.001). Among the patients with node-negative disease, 5-year OS decreased monotonically with increasing T stage (59.1%, 30.6%, 22.9%, 16.6%, and 8.0%, respectively; p < 0.001). In contrast, among the patients with node-positive disease, those with T1a–T1b tumors (< 10 mm) had worse 5-year OS than those with T1c tumors (7.4% vs 17.6%; adjusted hazard ratio, 0.70; 95% confidence interval, 0.50–0.97; p = 0.034) and similar survival compared with those who had T2, T3, or T4 tumors (9.7%, 8.2%, and 4.8%, respectively; p > 0.2 in all cases). Conclusions: Among patients with lymph node-positive PDAC, very small primary tumors are associated with decreased OS. This finding raises the possibility that small tumors capable of lymph node metastasis might represent more biologically aggressive cancers.