Alectinib hydrochloride is primarily used in the treatment of non-small cell lung cancer (NSCLC), specifically for patients whose cancer is anaplastic lymphoma kinase (ALK)-positive. It works by inhibiting the activity of the ALK protein, which is involved in the growth and spread of cancer cells. This targeted therapy is effective in slowing or stopping the progression of the disease, particularly in cases where the cancer has metastasized to the brain. It is often prescribed when other ALK inhibitors, such as crizotinib, have failed or are no longer effective. The drug is administered orally, making it convenient for patients to use as part of their ongoing treatment regimen. Its ability to cross the blood-brain barrier also makes it a valuable option for managing brain metastases associated with ALK-positive NSCLC.