Systemic immune-inflammation index prior to postoperative radiotherapy as a tool for outcome prediction in thymic...

The systemic immune-inflammation index (SII) is a prognostic biomarker in various solid tumors. However, the prognostic role of SII in thymic epithelial tumors (TETs) receiving adjuvant radiotherapy (RT) has not yet been explored. This study aims to assess the prognostic role of pre-RT SII in TET patients undergoing adjuvant RT.

A retrospective analysis was conducted on 37 patients treated with adjuvant RT for TETs between 2004 and 2023. The median adjuvant RT dose was 54 Gy (range, 50 to 70) delivered over 25-35 fractions. SII was calculated based on hemogram parameters within the two weeks preceding the start of RT, and its prognostic role was evaluated.

Median follow-up was 90 months (range, 12 to 230). The 5-year overall survival (OS) and disease-free survival (DFS) rates were 97.1% and 90.7%, respectively. The receiver operating characteristic analysis determined an optimal SII cut-off value of 916 for predicting recurrence (specificity, 67%; sensitivity, 71%). In univariate analysis, patients with an SII ≥916 had significantly lower 5-year OS (92.3% vs. 100%, p=0.028) and DFS (73.1% vs. 100%, p=0.011) compared to those with a SII below 916. In multivariable analysis, no variable remained statistically significant, likely due to limited events and small sample size.

Postoperative, pre-RT SII may have potential prognostic relevance in patients with TETs undergoing adjuvant RT. Elevated SII levels could be explored as a biomarker to help guide more individualized treatment and follow-up strategies; however, further studies are needed to validate these findings.