Background: Microscopic venous invasion (MVI) and the subsequent peripheral blood circulation of cancer cells are considered to be the primary route for systemic dissemination of pancreatic cancer.
Methods: Patients who underwent pancreatectomy for invasive ductal carcinoma of the pancreas between January 2007 and December 2015 were retrospectively reviewed. The prognostic significance of MVI was analyzed.
Results: A total of 352 patients underwent pancreatectomy for invasive ductal carcinoma of the pancreas. A pathologic examination showed MVI in 228 (64.5%) of the patients. The median survival time (MST) was 21 months for the patients with MVI and 58 months for those without MVI (p < 0.001). A multivariate analysis showed the following to be significant prognostic factors: non-administration of adjuvant chemotherapy [hazard ratio (HR) 2.37; p < 0.001], lymph node metastasis (HR 2.95; p = 0.001), CA19-9 value of 300 U/ml or higher (HR 1.70; p = 0.018), and MVI (HR 1.84; p = 0.011). The overall survival was clearly stratified into three groups; favorable (MST not reached in stage 1 or 2A without MVI; p = 0.867), moderate (30 months in stage 2A with MVI and 30 months in stage 2B without MVI; p = 0.528), and poor (19 months in stage 2B with MVI and 17 months in stage 4; p = 0.322). The differences between these three groups all were significant.
Conclusions: Approximately two-thirds of patients with radiologically resectable pancreatic cancer had MVI and were considered to have potentially systemic disease. This study identified MVI as one of the significant factors for a poor prognosis and a valuable complement of tumor-node-metastasis staging.