Chung et al. analyzed the transcriptomes of 515 single breast tumor cells from 11 patients with the luminal A, luminal B, HER2-positive, and triple-negative (ER/HER2/PR-negative) subtypes [25], and found that cells isolated from HER2-positive tumors were highly diverse and predominantly exhibited the HER2 and triple negative breast cancer (TNBC) phenotypes. The gene discussed is ERBB2; the disease is triple-negative breast carcinoma.