ERBB2 and breast cancer: Using the engineered MmPylRS•tRNAPyl pair, a 4-incorporated Ftn delivery system is designed to target a breast cancer overly expressed human epidermal growth factor receptor 2 (HER2-positive; Her2+), which is more malignant and has a higher incidence as well as mortality rate among all breast cancer subtypes (Piccart-Gebhart et al., 2005; Romond et al., 2005).