Methods are provided for predicting a response to an anti-PD-1 antibody or anti-PD-L1 antibody therapy based on a new biomarker and for evaluating a malignancy of cancer. The method for predicting a response of a subject to an anti-PD-1 antibody or anti-PD-L1 antibody therapy includes measuring an expression level of LAT1 in a sample collected from a cancer tissue of the subject; and predicting a response of the subject to the anti-PD-1 antibody or anti-PD-L1 antibody therapy based on the expression level of LAT1. The method for evaluating a malignancy of cancer in a subject includes staining a sample collected from a cancer tissue of the subject with an anti-LAT1 antibody and an anti-PD-L1 antibody; and evaluating a malignancy of the cancer in the subject based on a presence or absence of a LAT1-positive and PD-L1-positive site.