Neratinib is a tyrosine kinase inhibitorunder investigation for the treatment breast cancer and other solid tumours. It is in development for the treatment of early- and late-stage HER2-positive breast cancer. Like lapatinib and afatinib, it is a dual inhibitor of the human epidermal growth factor receptor 2 (Her2) and epidermal growth factor receptor (EGFR) kinases. Neratinib is an orally available, small, irreversible, pan-HER kinase inhibitor. HER-2-positive breast cancer is a breast cancer subtype with an increasing body of knowledge regarding potential targeted drug combinations that are significantly improving outcomes through a biologically tailored therapy approach; neratinib emerges as a promising tool in this context. This article reviews the molecular and clinical development of neratinib, an example of a covalent drug, from preclinical models to Phase III clinical trials, focusing on breast cancer treatment.