Pirtobrutinib is used in the treatment of certain blood cancers, particularly mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL). It functions as a highly selective inhibitor of Bruton's tyrosine kinase (BTK), a protein involved in B-cell receptor signaling that promotes the survival and spread of cancerous B-cells. Unlike earlier BTK inhibitors, pirtobrutinib is designed to be effective even in patients who have developed resistance mutations, such as the C481S mutation in BTK. This makes it a valuable option for patients who have relapsed or become refractory to prior BTK inhibitor therapies. It is taken orally and has shown promising response rates in clinical trials, offering a well-tolerated treatment alternative with manageable side effects. Its selectivity reduces off-target effects, contributing to a favorable safety profile.