Primary cilia are microtubule-based organelles that protrude from basal bodies and are involved in cell differentiation, sensory functions, and planar cell polarity. Although there are many studies examining the roles of primary cilia in the fields of embryology and physiology, few such studies have been carried out in the field of oncology, and the role of primary cilia in cancer cells is poorly understood. In this study, we identified primary cilia by immunofluorescence analysis in which primary cilia were visualized as green rods labeled with anti-acetylated α-tubulin adjacent to basal bodies detected as red dots labeled with anti-γ-tubulin. Primary cilia were found in human pancreatic cancer cell lines and in cancer cells in 25 of 100 pancreatic ductal carcinoma patients. In the clinical samples, most primary cilia in cancer tissue were observed in areas showing well-differentiated glandular structures. Patients whose cancers were primary cilia positive had a higher frequency of lymph node metastasis than those whose cancers were primary cilia negative (P =.016). Univariate analysis demonstrated that tumor size (P =.009), tumor grade (P =.001), lymph node metastasis (P =.008), and the presence of primary cilia (P =.002) correlated with overall survival. Multivariate analysis found that tumor grade (P <.001) and the presence of primary cilia (P =.001) were independent prognostic indicators. In conclusion, we showed that pancreatic cancer cells can form primary cilia and that the presence of primary cilia is significantly associated with the prognosis of pancreatic ductal adenocarcinoma.
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