ERBB2 and breast cancer: While differential gene expression among different subtypes of breast cancer have been widely used for assessing prognosis and predicting therapeutic response [8], The Cancer Genome Atlas (TCGA) network analyzed differential somatic mutations among the four breast cancer subtypes: luminal A, luminal B, HER2+, and basal like, and identified several significantly mutated genes that showed subtype-specific patterns of mutation [9].