目的:探讨细胞周期蛋白D1(Cyclin D1)标记指数在甲状腺乳头状癌(PTC)中有诊断意义的临界值及其临床意义。方法:回顾性分析2016年至2019年间诊断的311例PTC和120例甲状腺良性病变患者的临床病理学资料，对Cyclin D1、Claudin-1、CD56和Ki-67表达状况进行定量评估和相关统计分析。结果:在PTC和甲状腺良性病变患者中Cyclin D1标记指数平均值为39.2%±29.5%(范围1%～95%)。n Mann Whitney U检验显示，Cyclin D1在PTC和甲状腺良性病变患者标记指数均值差异有统计学意义(53.2%±22.5%对3.4%±4.2%, n P<0.01)。受试者工作特征(ROC)曲线法分析显示，诊断PTC的最佳临界值为19.0%，灵敏度为92.4%，特异度为99.2%；诊断甲状腺良性病变的最佳临界值为5.5%，灵敏度为96.0%，特异度为87.5%，ROC曲线下面积最大(0.989，95%n CI 0.982～0.995, n P<0.01)。以Cyclin D1标记指数≥20.0%(临界值19.0%)为阳性表达，联合Claudin-1和(或)CD56在诊断PTC时灵敏度为83.0%～95.2%，特异度为100.0%。Cyclin D1标记指数数值和癌结节直径、结节数量、淋巴结转移数目及TNM分期相关(n P0.05)。n 结论:Cyclin D1标记指数≥20.0%是诊断PTC的可靠指标，<5%提示可能甲状腺良性病变；Cyclin D1联合Claudin-1和(或)CD56可作为诊断PTC的重要辅助指标；Cyclin D1标记指数数值与PTC的侵袭转移能力有关。“,”Objective:To investigate the diagnostic cut-off value of Cyclin D1 labeling index and to discuss its clinical significance of the cut-off value in the papillary thyroid carcinoma(PTC).Methods:Clinicopathological data of 311 cases of PTC and 120 cases of benign thyroid lesions from year 2016 to 2019 were analyzed retrospectively, and the quantitative evaluation and statistical analysis of Cyclin D1 labeling index, Claudin-1, CD56, and Ki-67 index were carried out.Results:In PTC and benign thyroid lesions, the average value of cyclin D1 labeling index was 39.2%±29.5%(range 1%-95%). The differences in the average value(53.2%±22.5% n vs 3.4%±4.2%, n P<0.01) of Cyclin D1 labeling index in the PTC and benign thyroid lesions were statistically significant by Mann Whitney U test. The receiver operating characteristic curve analysis showed that the best diagnostic cut-off value of the PTC was 19.0%, the sensitivity was 92.4%, with the specificity 99.2%, and the best diagnostic cut-off value of the benign thyroid lesions was 5.5%, the sensitivity was 96.0%, the specificity was 87.5%, and the area under the curve was the largest(0.989, 95%n CI 0.982-0.995, n P<0.01). Cyclin D1 labeling index≥20.0%(the cut-off value 19.0%) was judged positive, the sensitivity and specificity of Cyclin D1 in combination with Claudin-1 and/or CD56 were 83.0%-95.2% and 100.0% in the differential diagnosis of PTC and benign thyroid lesions, respectively. There was a correlation between the Cyclin D1 labeling index and the number and diameter of tumor nodules, lymph node metastasis, and TNM staging(n P0.05).n Conclusions:Cyclin D1 labeling index≥20.0% is a reliable indicator of the diagnosis of PTC, while those<5% may be a benign thyroid lesions. The Cyclin D1 in combination with claudin-1 and/or CD56 can be used as an important auxiliary indicator for diagnosis of PTC. The Cyclin D1 labeling index is related to the invasion and metastasis ability of PTC.