Provided are gene signatures that are predictive of the sensitivity of a cancer or tumor to an MDM2i or an antagonist of the MDM2-p53 interaction. Differentially expressed genes in the provided gene signatures serve as biomarkers for determining and assessing the sensitivity of cancer and tumor samples to treatment or therapy with an MDM2i. Also provided are methods of determining MDM2i sensitivity of a test sample such as different cancer and tumor types and subtypes, based on the expression of genes in the MDM2i sensitive gene signatures in reference samples and the test sample even if all of the MDM2i sensitivities of the reference samples are unknown, and treating individuals with an MDM2i if their cancers are determined to be MDM2i-sensitive, based on the practice of the described methods. TP53 gene and p53 protein status can also be determined for the samples undergoing analysis for MDM2i sensitivity.
