ARQ 531 is a potent and selective inhibitor of Bruton’s tyrosine kinase (BTK), including both wild-type and C481S mutant forms. It is primarily investigated for the treatment of B-cell malignancies such as chronic lymphocytic leukemia (CLL), small lymphocytic lymphoma (SLL), and non-Hodgkin lymphoma (NHL). Unlike some other BTK inhibitors, ARQ 531 demonstrates activity against resistant mutants that commonly arise during treatment with first-generation inhibitors, making it a promising option for patients who have relapsed or become refractory to prior therapies. The compound has shown strong preclinical activity in inhibiting B-cell receptor signaling pathways, leading to reduced tumor cell proliferation and survival. It is designed to be orally bioavailable, allowing for convenient dosing in outpatient settings. Clinical trials are evaluating its safety, pharmacokinetics, and efficacy both as a monotherapy and in combination with other agents such as BCL-2 inhibitors or anti-CD20 antibodies. Due to its broad inhibition profile across several kinases involved in oncogenic signaling, ARQ 531 may also have potential applications in other hematologic cancers and inflammatory conditions, though its primary focus remains in oncology, particularly for resistant or relapsed B-cell cancers.