TAM family kinases as therapeutic targets at the interface of cancer and immunity

Novel treatment approaches are needed to overcome innate and acquired mechanisms of resistance to current anticancer therapies in cancer cells and the tumour immune microenvironment. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) are potential therapeutic targets in a wide range of cancers. In cancer cells, TAM RTKs activate signalling pathways that promote cell survival, metastasis and resistance to a variety of chemotherapeutic agents and targeted therapies. TAM RTKs also function in innate immune cells, contributing to various mechanisms that suppress antitumour immunity and promote resistance to immune-checkpoint inhibitors. Therefore, TAM antagonists provide an unprecedented opportunity for both direct and immune-mediated therapeutic activity provided by inhibition of a single target, and are likely to be particularly effective when used in combination with other cancer therapies. To exploit this potential, a variety of agents have been designed to selectively target TAM RTKs, many of which have now entered clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians, including an overview of the rationale for therapeutic targeting of TAM RTKs in cancer cells and the tumour immune microenvironment, a description of the current preclinical and clinical experience with TAM inhibitors, and a perspective on strategies for continued development of TAM-targeted agents for oncology applications. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) have diverse cancer-promoting functions in malignant cells as well as immune cells and other cell types in the tumour microenvironment, presenting an attractive opportunity for both direct and immune-mediated therapeutic activity manifest through inhibition of a single target. Accordingly, a variety of agents designed to selectively target TAM RTKs are entering clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians. The authors comprehensively review the various roles of TAM RTKs in cancer, the evidence supporting their potential as therapeutic targets, and the translational development of TAM-targeted agents as cancer treatments.