A companion diagnostic test is defined as an in vitro diagnostic device or an imaging tool whose use allows the safe application of a therapy. In-vitro Companion Diagnostic tests measure the expression or presence of a specific biomarker that is linked to a disease condition or therapy. This report provides an analysis of the companion diagnostic market for four major cancers in the US, the 5EU (France, Germany, Italy, Spain, and UK), Brazil, and the some of the Asia-Pacific (APAC) regions (Japan, China, and India), and identifies the unmet needs in this companion diagnostics market. This report analyses companion diagnostic tests used in breast, colorectal, melanoma and non-small cell lung cancer. This report also discusses physician attitudes towards current companion diagnostic tests, and the future of companion diagnostic tests. This report focuses on the major test kits that are supplied to pathology laboratories.