Patient derived xenografts (PDX) are models of cancer where the tissue or cells from a patient's tumor are implanted into an immunodeficient or humanized mouse.[1] It is a form of xenotransplantation. PDX models are used to create an environment that allows for the continued growth of cancer after its removal from a patient. In this way, tumor growth can be monitored in the laboratory, including in response to potential therapeutic options.[1] Cohorts of PDX models can be used to determine the therapeutic efficiency of a therapy against particular types of cancer, or a PDX model from a specific patient can be tested against a range of therapies in a 'personalized oncology' approach.