The objective of this study is to detect the expression of midkine (MK) in papillary thyroid cancer (PTC) and to evaluate whether MK expression is associated with clinicopathological features and BRAF mutation in PTC. The expression of MK in samples from 200 cases of PTC, 60 cases of adenomatoid nodule of thyroid, and 40 samples of tumor-adjacent normal thyroid tissue were assessed with immunohistochemistry. The BRAF mutation was detected by direct sequencing. The relationships between MK expression and the clinicopathological features of PTC and BRAF mutation were analyzed. The results demonstrated that MK was not expressed in tumor-adjacent normal tissue. The positive expression rates and MK scores were both higher in PTC than in adenomatoid nodule (positive expression rates: 88 vs. 8.3 , P < 0.001; MK scores: 2.02 +- 0.93 vs. 0.08 +- 0.28, P < 0.001). The expression level of MK in PTC with extrathyroidal invasion, lymph node metastasis, or stage III/IV was significantly higher than that in PTC without such biological features (all P < 0.01). The overall prevalence of BRAF mutation was 66.5 in PTC.
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