There are several limitations in this study. First, it was a retrospective study. We could not obtain sufficient information regarding 9.2% and 11.6% of patients in the training and validation sets, respectively, thereby resulting in some bias in the results. Second, the measurement methods for serum AST and ALT in Japan are different from those in other countries. Both the JSCC and IFCC methods should be used and compared in future studies. Third, HPV status should be considered for analyzing oropharyngeal cancer. Finally, the mechanisms of how the AST/ALT ratio is associated with survival of patients with HNSCC remain to be studied.