Companion diagnostic tests for treatment of lung cancer patients: what are the current and future challenges?

Introduction: Companion diagnostic tests (CDXs) are considered mandatory for decision-making for treatment with targeted therapies in thoracic oncology. The emergence of immunotherapy has also given rise to the development of CDXs. Some CDXs, in particular PD-L1 immunohistochemistry tests, have been questioned and re-examined for use with new combination therapies that are being evaluated in clinical trials. Current questions include: Can we establish therapeutic indications in thoracis oncology without CDXs? Would the addition of new tests benefit patient outcome? Areas covered: This review covers the use of CDXs for decision-making in the treatment of lung cancer but also covers the limits of certain tests. It discusses the major challenges for present and future development of CDXs in daily practice. Expert opinion: CDXs can predict the efficacy of drugs if crucial steps in development and validation are fully controlled. Future development of CDXs must consider the detection of biomarkers of resistance and toxicity that are complementary to CDXs predicting therapeutic drug efficacy. Certain CDXs that have already been developed may be of interest for new indications in the field of thoracic oncology.