To investigate the prognostic value of pre-treatment skeletal muscle index at the third lumbar vertebra (L3-SMI) for survival in patients with cervical cancer, and to analyze its predictive performance across different International Federation of Gynecology and Obstetrics (FIGO) stages.

Clinical data and imaging studies of patients with cervical cancer diagnosed and treated at Hunan Cancer Hospital from January 2014 to December 2019 were retrospectively collected. Skeletal muscle was segmented at the mid-vertebral level of the third lumbar vertebra, and skeletal muscle area (SMA) was measured. L3-SMI was calculated as SMA divided by body surface area (BSA). The optimal cut-off value of L3-SMI for predicting overall survival (OS) in cervical cancer patients was determined using receiver operating characteristic (ROC) curve analysis. Survival differences between patients with different L3-SMI levels were compared using the Kaplan-Meier method and Log-Rank test. The independent prognostic value of L3-SMI was analyzed using the Cox proportional hazards regression model.

A total of 207 patients were enrolled in this study. Survival analysis showed that L3-SMI was not significantly correlated with OS in the early-stage group (FIGO stages I and IIA, P>0.05), but was significantly correlated with OS in the advanced-stage group (FIGO stages IIB, III and IV, P<0.05). The optimal cut-off value of L3-SMI for predicting OS in advanced-stage patients was 39.8 cm²/m², with an area under curve (AUC) of 0.668. Accordingly, 101 advanced-stage patients were divided into the high L3-SMI group (≥39.8 cm²/m², n=51) and the low L3-SMI group (<39.8 cm²/m², n=50). Kaplan-Meier analysis demonstrated that patients in the high L3-SMI group had significantly better OS than those in the low L3-SMI group, with a statistically significant difference (Log-Rank χ²=8.20, P=0.004 2). Multivariate Cox regression analysis revealed that low L3-SMI remained an independent risk factor for OS in advanced-stage patients after adjusting for age, FIGO stage, and pathological type (HR=2.561, 95%CI: 1.040~6.336, P=0.039).

Pre-treatment L3-SMI is an independent prognostic factor for survival in patients with advanced-stage cervical cancer (FIGO stage IIB and above), and this biomarker has clinical value in predicting the prognosis of advanced cervical cancer patients.