BACKGROUND: Immune checkpoint inhibitors (ICIs) are playing a significant role in the treatment of hepatocellular carcinoma (HCC). This study aims to explore the prognostic value of alpha-fetoprotein (AFP) and initial tumor shape irregularity in patients treated with ICIs. METHODS: In this retrospective, multi-center study, 296 HCC patients were randomly divided into the training set and the validation set in a 3:2 ratio. The training set was used to evaluate prognostic factors and to develop an easily applicable ATSI (AFP and Tumor Shape Irregularity) score, which was verified in the validation set. RESULTS: The ATSI score was developed from two independent prognostic risk factors: baseline AFP ≥ 400 ng/ml (HR 1.73, 95% CI 1.01-2.96, P = 0.046) and initial tumor shape irregularity (HR 1.94, 95% CI 1.03-3.65, P = 0.041). The median overall survival (OS) was not reached (95% CI 28.20-NA) in patients who met no criteria (0 points), 25.8 months (95% CI 14.17-NA) in patients who met one criterion (1 point), and 17.03 months (95% CI 11.73-23.83) in patients who met two criteria (2 points) (P = 0.001). The median progression-free survival (PFS) was 10.83 months (95% CI 9.27-14.33) for 0 points, 8.03 months (95% CI 6.77-10.57) for 1 point, and 5.03 months (95% CI 3.83-9.67) for 2 points (P <
0.001). The validation set effectively verified these results (median OS, 37.43/24.27/14.03 months for 0/1/2 points, P = 0.028
median PFS, 13.93/8.30/4.90 months for 0/1/2 points, P <
0.001). CONCLUSIONS: The ATSI score can effectively predict prognosis in HCC patients receiving ICIs.