To investigate the correlation between thymic epithelial tumors and the systemic immune-inflammation index based on histological classification of World Health Organization.

From January 2017 to December 2019, 46 cases of thymic epithelial tumors confirmed by operation and pathology were analyzed retrospectively. According to the histological classification of WHO published in 2015, data were divided into low risk thymoma (LRT including type A, AB and B1), high risk thymoma (HRT including type B2 and B3), thymic carcinoma (TC). Patients of benign thymic tumor (BTT) treated by operation at the same time were reviewed as a control group. For all patients, their peripheral blood platelet (P), neutrophil (N), and lymphocyte (L) counts were obtained 4 days before the operation. Indexes were calculated according to SII=P×N/L. The differences between the groups were compared, and the correlation with the degree of malignancy was calculated.

A total of 46 patients with thymic epithelial tumors (20 in the low-risk group, 19 in the high-risk group and 7 in the thymic cancer group) and 34 patients in the control group were included in the research. The SII value of the TC group was significantly higher than the other three groups, P=0.009. SII was significantly correlated with the malignancy of thymic epithelial tumors, with a correlation coefficient of 0.244(P=0.032).

Based on the histological classification of WHO, the malignant degree of thymic epithelial tumor is significantly correlated with the systemic immune- inflammatory index. SII can be used to clinically predict the malignancy of thymic epithelial tumors.