AP26113 is primarily used in the treatment of non-small cell lung cancer (NSCLC), particularly for patients with specific genetic mutations such as ALK (anaplastic lymphoma kinase) and ROS1 rearrangements. It functions as a tyrosine kinase inhibitor, targeting and blocking the activity of these mutated proteins, which are responsible for the uncontrolled growth of cancer cells. This helps in slowing down or stopping the progression of the disease. Additionally, it is being investigated for its potential efficacy in other types of cancers where ALK or ROS1 mutations are present. The compound is often considered for patients who have developed resistance to other similar therapies, offering an alternative treatment option.