ObjectiveTo investigate the effects of lenvatinib combined with transarterial chemoembolization (TACE) and programmed death protein-1 (PD-1) monoclonal antibody (Abbreviated as LEN-TAP regimen) on residual liver volume and surgical safety in intermediate and advanced hepatocellular carcinoma (HCC). MethodsThe clinicopathologic data of patients with intermediate and advanced HCC were collected retrospectively, who underwent the LEN-TAP conversion therapy and surgical resection in the Department of Liver Surgery, West China Hospital, Sichuan University from October 2020 to December 2021. The total liver volume, tumor volume, and residual liver volume of the patients before and after conversion therapy were analyzed. ResultsA total of 48 patients were included, 26 of whom had partial remission and 22 had stable disease, the objective response rate was 54.2% (26/48) according to the Response Evaluation Criteria in Solid Tumours 1.1 after conversion therapy. Before and after conversion therapy, the total liver volumes including tumor were (1 607.15±712.22) mL and (1 558.03±573.89) mL [mean difference (MD) and 95% confidence interval (CI)=–57.42(–134.30, 19.46), t=–1.503, P=0.140], the total liver volumes excluding tumor tissue were (1 095.28±227.60) mL and (1 260.31±270.71) mL [MD(95%CI)=165.03(128.13, 201.93), t=8.997, P<0.001], the tumor volumes were 260.25(107.75, 699.50) mL and 121.73 (33.00, 332.88) mL [MD(95%CI)=–222.45(–296.46, –148.44), Z=–5.641, P<0.001], and the residual liver volumes were (493.62±154.51) mL and (567.83±172.23) mL [MD(95%CI)=74.21(54.64, 93.79), t=7.627, P<0.001], respectively. The increase rates of tumor volume and residual liver volume after conversion therapy were (–53.34±33.05)% and (16.34±15.16)%, respectively. The conversional resections were successfully completed in all patients, with 13 (27.1%) cases experiencing postoperative complications and without occurrence of postoperative liver failure. ConclusionThe data analysis results of this study indicate that the LEN-TAP conversion therapy can shrink tumor volume and increase the residual liver volume for patients with intermediate and advanced HCC, which helps to improve the safety of conversion resection.