Predictive biomarkers being used as companion diagnostic agents will help to avoid critical failures of drug treatment due to a lack of efficacy. Therefore, the predictive biomarkers can reduce the number of patients needed to demonstrate the efficacy in clinical trials by enriching the populations with biomarker-positive patients. In addition, this allows avoiding adverse effects by unnecessary treatment. The presence or absence of the target molecule-related gene expression can be such a biomarker. As an example, aberrant activation of anaplastic lymphoma kinase (ALK) after being fused with echinoderm microtubule-associated protein-like 4 (EML4) shows oncogenic potential and the underlying genetic rearrangement is the oncogene in a small subset of non-small cell lung cancer (NSCLC). ALK inhibitors and companion diagnostic agents to detect the fusion gene have been developed simultaneously and approved for ALK fusion gene-positive NSCLC. This represented a landmark in oncology drug development and a significant step toward precision medicine. In this presentation, the current situation of predictive biomarker-driven drug development will be discussed.