Epertinib hydrochloride is primarily used in the treatment of non-small cell lung cancer (NSCLC), particularly in cases where the cancer has specific mutations in the epidermal growth factor receptor (EGFR). It is an EGFR tyrosine kinase inhibitor that targets and blocks the activity of mutated EGFR proteins, which are often responsible for the uncontrolled growth of cancer cells. This helps to slow down or stop the progression of the disease. It is especially effective for patients who have developed resistance to other EGFR inhibitors, such as gefitinib or erlotinib, due to the T790M mutation. Epertinib hydrochloride is administered orally, making it a convenient option for patients undergoing long-term treatment. Its ability to penetrate the blood-brain barrier also makes it a valuable option for treating NSCLC that has metastasized to the brain. Clinical trials have shown promising results in improving progression-free survival and overall response rates in patients with advanced NSCLC.