Entrectinib is primarily used in the treatment of certain types of cancer, particularly those involving specific genetic mutations. It is effective against cancers that exhibit NTRK gene fusions, which are found in various solid tumors such as lung cancer, colorectal cancer, and breast cancer. Additionally, it is used for treating non-small cell lung cancer (NSCLC) that is ROS1-positive. The drug works by inhibiting the activity of the proteins produced by these gene mutations, thereby slowing or stopping the growth of cancer cells. Entrectinib is particularly valued for its ability to cross the blood-brain barrier, making it effective in treating cancers that have metastasized to the brain. Its targeted approach helps minimize damage to healthy cells, reducing some of the side effects commonly associated with traditional chemotherapy.