A method for testing a patient for the presence or absence of an on-treatment biomarker that predicts that the patient is likely to have an anti-tumor response to treatment with a PD-1 antagonist, which comprises: (a) obtaining a sample of total intracellular RNA that has been isolated from a baseline blood sample collected from the patient, (b) measuring the baseline raw RNA expression level in the isolated RNA for each gene in a gene signature, (c) normalizing the measured baseline raw RNA expression levels (d) calculating a baseline signature score for the gene signature from the normalized RNA expression levels, (e) obtaining a sample of total intracellular RNA that has been isolated from a post-dose blood sample collected from the patient, (f) measuring the post-dose raw RNA expression level in the isolated RNA for each gene in the gene signature, (g) normalizing each of the measured post-dose raw RNA expression levels; (h) calculating a post-dose signature score for the gene signature from the normalized RNA expression levels (i) calculating a post-dose signature score for the gene signature from the measured RNA expression levels, and (j) comparing the post-dose score to the baseline score, and (k) classifying the patient as biomarker positive or biomarker negative; wherein the patient is classified as biomarker positive if the post-dose signature score is greater than the baseline signature score the patient and the patient is classified as biomarker negative if the post-dose signature score is equal to or less than the baseline signature score, wherein steps b-d may be performed before, concurrently with, or after steps f-h, and wherein the gene signature comprises a set of genes selected from the group consisting of: (i) PD-L1, PD-L2, LAG3, STAT1, and CXCL10; (ii) PD-L1, PD-L2, LAG3, STAT1, CXCL10 and CLEC10a; (iii)CXCL9, CXCL10, HLA-DRA, IDO1, and STAT1; (iv)CXCL9, CXCL10, HLA-DRA, IDO1, IFNG, and STAT1; (v) CCR5, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, PRF1 and STAT1; and (vi)CCR5, CLEC10a, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, LAG3, PD-L1, PD-L2, PRF1, and STAT1. (a) obtaining a sample of total intracellular RNA that has been isolated from a baseline blood sample collected from the patient, (b) measuring the baseline raw RNA expression level in the isolated RNA for each gene in a gene signature, (c) normalizing the measured baseline raw RNA expression levels (d) calculating a baseline signature score for the gene signature from the normalized RNA expression levels, (e) obtaining a sample of total intracellular RNA that has been isolated from a post-dose blood sample collected from the patient, (f) measuring the post-dose raw RNA expression level in the isolated RNA for each gene in the gene signature, (g) normalizing each of the measured post-dose raw RNA expression levels; (h) calculating a post-dose signature score for the gene signature from the normalized RNA expression levels (i) calculating a post-dose signature score for the gene signature from the measured RNA expression levels, and (j) comparing the post-dose score to the baseline score, and (k) classifying the patient as biomarker positive or biomarker negative; wherein the patient is classified as biomarker positive if the post-dose signature score is greater than the baseline signature score the patient and the patient is classified as biomarker negative if the post-dose signature score is equal to or less than the baseline signature score, wherein steps b-d may be performed before, concurrently with, or after steps f-h, and wherein the gene signature comprises a set of genes selected from the group consisting of: (i) PD-L1, PD-L2, LAG3, STAT1, and CXCL10; (ii) PD-L1, PD-L2, LAG3, STAT1, CXCL10 and CLEC10a; (iii)CXCL9, CXCL10, HLA-DRA, IDO1, and STAT1; (iv)CXCL9, CXCL10, HLA-DRA, IDO1, IFNG, and STAT1; (v) CCR5, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, PRF1 and STAT1; and (vi)CCR5, CLEC10a, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, LAG3, PD-L1, PD-L2, PRF1, and STAT1. (i) PD-L1, PD-L2, LAG3, STAT1, and CXCL10; (ii) PD-L1, PD-L2, LAG3, STAT1, CXCL10 and CLEC10a; (iii)CXCL9, CXCL10, HLA-DRA, IDO1, and STAT1; (iv)CXCL9, CXCL10, HLA-DRA, IDO1, IFNG, and STAT1; (v) CCR5, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, PRF1 and STAT1; and (vi)CCR5, CLEC10a, CXCL9, CXCL10, CXCL11, GZMA, HLA-DRA, IDO1, IFNG, LAG3, PD-L1, PD-L2, PRF1, and STAT1.