目的探讨重症肌无力(MG)合并胸腺瘤的临床特点和细胞核增殖相关抗原(PCNA)的表达。方法选择25例伴有MG的胸腺瘤患者(MG组)和25例不伴有MG的胸腺瘤患者(非MG组),采用免疫组化法检测患者胸腺瘤组织中PCNA的表达,阳性为棕黄色颗粒;记录在放大100倍的油镜下随机计数1000个肿瘤细胞中的阳性细胞率。结果MG组中5例发生肌无力危象,其中1例死亡。伴重症肌无力的瘤性细胞群主要含有PCNA低表达的细胞。结论伴重症肌无力的胸腺瘤组织恶性程度相对较低,淋巴细胞型的胸腺瘤患者易伴发重症肌无力。 Objective To investigate the clinical features and the expression of proliferating cell nuclear antigen (PCNA) in myasthenia gravis (MG) combined with thymoma. Methods Twenty-five thymoma patients with MG (MG group) and 25 thymoma patients without MG (non-MG group) were enrolled in this study. The expression of PCNA in thymoma tissues was detected by immunohistochemistry Yellow particles; recorded in a magnification of 100 times the oil microscope randomly counting the number of 1000 tumor cells in the positive cells. Results In MG group, 5 cases of myasthenia gravis crisis occurred, of which 1 case died. The neoplastic cell mass with myasthenia gravis mainly contains cells with low expression of PCNA. Conclusions Thymoma with myasthenia gravis has a relatively low degree of malignancy, and patients with lymphocytic thymoma are more likely to develop myasthenia gravis.