Simple SummaryAlthough sarcopenia-related factors, including decreased skeletal muscle index (SMI), have been reported to affect therapeutic efficacy and the occurrence of adverse events in sorafenib or lenvatinib treatment for hepatocellular carcinoma (HCC), there is considerably less evidence regarding the relationship between SMI and prognosis in the HCC patients treated with atezolizumab plus bevacizumab (atezo/bev) therapy. Furthermore, there are no reports of muscle strength, including grip strength (GS), which is essential for an accurate diagnosis of sarcopenia. This is the first study to show the relationship between sarcopenia, diagnosed by decreased GS and SMI, and clinical outcomes in atezo/bev therapy, with novel evidence having a strong impact. The presence of sarcopenia is significantly associated with shorter overall survival with the occurrence of adverse events and decreased liver function. Monitoring of both GS and SMI is useful for assessing the general condition and predicting prognosis in HCC patients treated with atezo/bev therapy.AbstractAlthough there have been advances in the prevention and diagnosis of hepatocellular carcinoma (HCC) in recent years, many HCC patients are still diagnosed with advanced stage. Systemic therapy is indicated for unresectable HCC (uHCC) with major vascular invasion and/or extrahepatic metastases, and the atezolizumab plus bevacizumab (atezo/bev) combination is currently recommended as first-line treatment for uHCC. Recently, sarcopenia-related factors, including decreased skeletal muscle index (SMI), have been reportedly associated with prognosis in uHCC patients treated with sorafenib or lenvatinib. There are few reports on muscle strength assessments, including grip strength (GS), despite their importance in accurate sarcopenia diagnosis, and furthermore, there is no evidence regarding atezo/bev therapy. In this study, we investigated whether sarcopenia affects the clinical outcome of atezo/bev therapy. This study included 64 uHCC patients on atezo/bev therapy and assessed their GS and SMI, and SMI was measured using bioelectrical impedance analysis (BIA). We diagnosed sarcopenia based on GS and BIA-SMI and compared the clinical outcomes in the sarcopenia and non-sarcopenia groups. Of these patients, 28 had sarcopenia, and 36 had non-sarcopenia. Adverse events (AEs) frequently occurred, and the albumin-bilirubin score significantly decreased after atezo/bev therapy in the sarcopenia group than in the non-sarcopenia group. The median progression-free survival was 4.7 (0.4–26.4) and 10.6 (1.1–24.5) months in the sarcopenia and non-sarcopenia groups, respectively. The median overall survival (OS) was 12.6 (1.4–27.7) months in the sarcopenia group and was not reached in the non-sarcopenia group, indicating a significant difference in the Kaplan-Meier survival curves for both groups (p< 0.01). In multivariate analysis, sarcopenia was significantly associated with OS. In conclusion, sarcopenia was significantly associated with poor clinical outcomes based on the occurrence of AEs and decreased liver function in uHCC patients on atezo/bev therapy. GS and SMI are important parameters for accurately diagnosing sarcopenia.