Background: Pancreatic ductal adenocarcinoma (PDAC) is still one of the most fatal cancers, although its prognosis has improved recently with the introduction of multimodal therapy. To further develop effective treatment for PDAC, establishment of prognostic indicators for patients receiving multimodal therapy is essential. Methods: Sixty-eight patients receiving curative extended resection combined with preoperative chemoradiation and postoperative chemotherapy for primary PDAC were selected. Immunohistochemistry using anti-CD74 antibody on paraffin-embedded tissue samples was performed, and cases were divided into two groups according to the ratio of CD74-positive cells: expression level I, CD74-positive cells <70%; level II, CD74-positive cells ≥70%. The correlation of CD74 expression level with clinicopathological features and overall survival was evaluated. Results: Forty-seven (69.1%) and 21 (30.9%) patients showed level I and II CD74 expression, respectively. Patients with level II CD74 expression showed a higher rate of lymphatic permeation (P = 0.04) and perineural invasion (P = 0.01) compared with those with level I expression. Patients with level I CD74 expression had a significantly better survival rate than those with level II (P = 0.003). Among the patients with pathological tumor-node-metastasis stages I and II, those with level I CD74 expression showed a significantly better prognosis than those with level II (P = 0.006). Multivariate analysis revealed CD74 expression level and vascular permeation of carcinoma as independent prognostic indicators. Conclusions: CD74 expression proved as a useful prognostic indicator for PDAC treated with multimodal therapy.
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