Patient Characteristics
The study included 268 patients meeting the inclusion criteria, detailed in Table 1. Both cohorts, training and validation, were predominantly male (training: 90.32%, validation: 85.14%) and showed a high prevalence of advanced-stage HCC, as classified by BCLC (training: 94.62%, validation: 91.43%). A majority of patients tested positive for AFP and HBV, with compensated liver function. The training cohort had a lower incidence of extrahepatic metastasis (30.11% vs. 47.43%, P = 0.006) but a higher rate of HBsAg positivity (89.25% vs. 74.86%, P = 0.005) and macrovascular tumor thrombus (68.82% vs. 54.29%, P = 0.021) compared to the validation cohort. Additionally, the training group had a higher proportion of patients with lower PLR (76.34% vs. 64.00%, P = 0.039). No significant differences were noted in the distribution of patients based on SII and NLR between the cohorts.
The training cohort showed a slightly higher objective response rate (ORR) of 30.1% compared to 29.7% in the validation cohort (Supplementary Fig. S2A). Median PFS was longer in the training group (7.37 months, 95% CI: 2.76 – 11.96) than in the validation cohort (6.50 months, 95% CI: 4.83 – 8.17), as depicted in Supplementary Figures S2B and S2C. Similarly, the training cohort exhibited a higher median OS of 17.7 months (95% CI: 14.7-29.2) compared to 16.77 months (95% CI: 13.18 – 20.35) in the validation group, as shown in Supplementary Figures S2D and S2E.
Association Between SII and Clinicopathologic Parameters
An optimal cutoff point for the SII of 752*109 was identified in the training cohort using X-Tile analysis. Patients were subsequently categorized into two groups: SII ≤752*109 or >752*109 for further analysis. Higher SII values (>752*109) correlated significantly with extrahepatic metastasis in the training cohort (P = 0.011) and with an increased likelihood of vascular tumor thrombus in the validation cohort (P = 0.019), as detailed in Table 2.
Prognostic Significance of SII in the Training Cohort
Building on previous findings regarding the prognostic value of the NLR in T+A treated HCC patients, this study focused on assessing the reliability of SII in a similar cohort from Zhongshan Hospital, Fudan University. Univariate analysis revealed SII as a significant prognostic factor for both PFS (HR = 2.296, 95% CI = 1.264 - 4.170, P = 0.006, Supplementary table S2) and OS (HR = 2.692, 95% CI = 1.395 - 5.196, P = 0.003, Supplementary table S3), outperforming other clinical factors. PLR and NLR were also significant for OS, as previously reported. Other factors such as age, gender, Child–Pugh score, alanine aminotransferase (ALT) level, α-fetoprotein (AFP), macrovascular tumor thrombus, extrahepatic metastasis, and CNLC stage showed limited prognostic impact for PFS or OS. Multivariate analysis confirmed SII as an independent prognostic factor for both PFS and OS.
Kaplan–Meier analysis demonstrated that lower SII was associated with longer PFS and OS (Fig. 1A - B). Patients with SII ≤ 752*109 had a median PFS of 11.6 months and OS of 25.5 months, whereas those with SII > 752*109 had 5.1 months and 12 months, respectively. Further analysis for PLR and NLR indicated that lower PLR correlated with longer PFS and OS (Supplementary Fig. S3A - B), while lower NLR only showed a significant association with OS (Supplementary Fig. S3C - D). Patients with lower SII had better ORR (34.72% vs. 9.52%; P = 0.019; Fig. 1C; Supplementary Table S1). NLR and PLR had limited predictive ability for ORR (Supplementary Fig. S3E - F). Additionally, responders tended to have lower SII scores than non-responders (337.0 vs. 613.3, P < 0.001, Fig. 1D). The area under the curve (AUC) values for SII, NLR, and PLR in predicting ORR, OS, and PFS suggested that SII was the strongest factor among them (Fig. 1E - G).
Validation of the SII in an Independent Cohort
The prognostic relevance of SII was further validated in an independent cohort of 175 patients treated with TKIs plus PD-(L)1 inhibitors. The validation cohort's findings were consistent with the initial training cohort, confirming the strong association of SII with PFS and OS in both univariate and multivariate analyses (Supplementary Table S2 - 3). Patients with SII lower than 752*109 showed a higher response rate and benefited more from immune-based therapy, evidenced by prolonged PFS and OS (Fig. 2A - C). Responders were characterized by significantly lower SII scores compared to non-responders (427.8 vs. 649.4, P = 0.005, Fig. 2D). The predictive function of PLR for PFS was not observed in this cohort (Supplementary Fig. S4). The AUC values for SII in predicting ORR, PFS, and OS were superior to other clinical indices (Fig. E - G).
The Prognostic Significance of SII in HCC Patients with Negative AFP Subgroups
Further investigation into the prognostic value of SII in AFP-negative HCC patients revealed that lower SII scores in the training cohort significantly improved PFS and OS (Fig. 3A - B). The validation cohort showed similar findings, confirming the prognostic relevance of SII for PFS and OS in AFP-negative patients (Fig. 3C - D). These results highlight SII's potential as a valuable biomarker in this specific patient subgroup.
Patients with Lower SII Scores Tend to Have Higher Effective T Cell Ratio In Peripheral Blood
Exploring the relationship between SII scores and immune response, the study focused on lymphocyte composition, particularly T cells, given their established significance in cancer immune-based therapy 22. Patients with lower SII scores exhibited higher T cell ratios in their lymphocytes in both cohorts (P = 0.008, P < 0.001, respectively, Fig. 3E - F). According to the flow cytometry results in our previous study 23, we matched 33 patients in TKIs plus PD-(L)1 antibody group. Results showed that patients in lower SII group tended to have higher CD8+T cell and GranzymeB+CD8+T cell number in peripheral blood (P = 0.013, P = 0.034, respectively, Fig. 3G - H). These findings underscore the potential influence of SII on immune functionality, especially considering the crucial role of T cells in mediating anti-tumor effects.