Theliatinib (HMPL-309) is primarily used in the field of oncology as a targeted therapy for cancer treatment. It functions as an inhibitor of the epidermal growth factor receptor (EGFR), which is often overexpressed or mutated in various types of cancers, including non-small cell lung cancer (NSCLC). By blocking EGFR signaling, it helps to inhibit tumor growth and proliferation. This makes it a potential therapeutic option for patients with EGFR-driven cancers, particularly those who may have developed resistance to first-generation EGFR inhibitors. Clinical trials are ongoing to evaluate its efficacy, safety, and potential as part of combination therapies in cancer treatment regimens.