Neratinib is primarily used in the treatment of HER2-positive breast cancer. It is an irreversible tyrosine kinase inhibitor that targets HER2 and EGFR, making it effective in blocking the signaling pathways that promote cancer cell growth. It is often prescribed as an extended adjuvant therapy for patients who have previously undergone trastuzumab-based treatment to reduce the risk of cancer recurrence. Additionally, it is being investigated for its potential in treating other HER2-driven cancers, such as metastatic breast cancer and certain types of non-small cell lung cancer. Its ability to cross the blood-brain barrier also makes it a candidate for treating HER2-positive brain metastases.