In the treatment of hepatocellular carcinoma (HCC) with transarterial radioembolization (TARE), identifying reliable biomarkers for predicting survival outcomes remains a critical challenge. We aimed to address this gap by investigating the significance of serum cytokines associated with inflammation as potential biomarkers for the selection of patients for TARE. Our retrospective study involved 161 patients diagnosed with HCC who underwent Y90 radioembolization at our medical center between 2010 and 2020. Serum samples from a subset of 78 patients were retrospectively analyzed to determine the concentrations of pro-inflammatory cytokines. The results from the prospective SORAMIC trial were used for independent validation. With a median overall survival of 36 weeks (range 4-436), our study showed the strongest correlation between 12-week survival and IL-8 levels before treatment (p < 0.001), while other relevant interleukins, interferon-α2, INF-γ, TNF-α and MCP-1 were not associated with survival. IL-8 levels below the cut-off of 190 pg/mL were significantly associated with increased 12-week and 24-week survival, with hazard ratios of 19.01 (95% CI: 2.29-157.89) and 2.57 (95% CI: 1.05-6.31), respectively (p = 0.006 and p = 0.039, respectively). In the adjusted multivariate analysis, the 190 pg/mL cut-off for IL-8 remained independently associated with 12- (p = 0.011) and 24-week survival (p = 0.039). Similarly, the SORAMIC population showed a strong association between IL-8 levels and 36-week survival (p = 0.03). Our study emphasizes the pivotal role of IL-8 as a valuable parameter, demonstrating its potential for predicting treatment outcomes and assessing liver function in patients with HCC undergoing TARE. The robustness of these findings warrants further validation.