An independent dataset was used to validate the prognostic effect of the AST/ALT ratio. Characteristics of patients between the training and validation sets were significantly different in the distribution of primary sites, T classification, treatment modality, and AST level (Table 1). The validation set included more number of female patients, patients with T4 disease, and patients with oral cavity primary. In the training set, the most employed treatment was CRT, while in the validation set, it was surgery. In the validation set, the median follow-up period for surviving patients was 59.9 (range, 25.9–111.4) months. According to the classification that was determined using the training set, the distribution of each group in the validation set was as follows: stage III, 47 patients (28%); stage IVA with low AST/ALT, 97 patients (58%); stage IVA with high AST/ALT, 14 patients (8%); and stage IVB, 9 patients (5%). The overall survival curve according to this classification is shown in Fig 2.