A key component of precision medicine is companion diagnostics that measure biomarkers e.g. protein expression, gene amplification or specific mutations. For example, most of the recent attention concerning molecular cancer diagnostics has been focused on the biomarkers of response to therapy, such as KRAS mutations in metastatic colorectal cancer, EGFR mutations in advanced Non-small cell lung cancer, and BRAF mutations in metastatic malignant melanoma. The presence or absence of these markers is directly linked to the response rates of particular targeted therapies with small-molecule kinase inhibitors or antibodies. Therefore, testing for these markers has become a critical step in the target therapy of the above-mentioned tumors. A companion diagnostic device is essential for the safe and effective use of a corresponding therapeutic product. The validation of a new companion diagnostic device includes both measurement and clinical validation as it is intended to be used. In this webinar we aim to cover the following important aspects of companion diagnostic device clinical validation (1) different indications for use and study designs (2) companion diagnostic device clinical performance measures (3) companion diagnostic device bridging study (4) follow-on companion diagnostic device (5) the impact of companion diagnostic device measurement performance on clinical validation of precision medicine including samples size calculation.