A recent study used isogenic knock-in ERBB2 mutations in ER+ MCF-7 cells and xenografts, and discovered that ERBB2 mutations can hyperactivate the HER3/PI3K/AKT/mTOR axis, leading to anti-estrogen resistance in ER+ BC (Croessmann et al., 2019). The gene discussed is ERBB3; the disease is breast cancer.