The present invention relates to somatic ErbB3 mutations in cancer, including methods for identifying, diagnosing, and prognosing ErbB3 cancer, and methods for treating cancer, including a subpopulation of patients. [Selection] Figure 4本発明は、癌における体細胞ErbB3変異に関し、ErbB3癌を特定、診断、および予後診断する方法、ならびに癌を治療する方法を含み、患者のある亜集団を含む。【選択図】図4