LDK378.2HCl is primarily used in the treatment of non-small cell lung cancer (NSCLC), particularly in patients with anaplastic lymphoma kinase (ALK) positive mutations. It works by inhibiting the ALK enzyme, which is crucial for the growth and survival of cancer cells in these patients. This targeted therapy helps to slow down or stop the progression of the disease, offering a more effective treatment option compared to traditional chemotherapy. It is often prescribed when other ALK inhibitors have failed or are not suitable, providing a critical line of defense for patients with advanced or metastatic NSCLC.