Annexin A1 is the first characterized member of the annexin family of proteins and is able to bind to cellular membranes in a calcium-dependent manner, promoting membrane fusion and endocytosis. Annexin A1 has anti-inflammatory properties and inhibits phospholipase A2 activity. Annexin A1 also has roles in many diverse cellular functions, such as membrane aggregation, inflammation, phagocytosis, proliferation, apoptosis, and tumorigenesis and cancer development. ANXA1 is strongly expressed on the cell membrane and occasionally in the cytoplasm of tumor cells in 97% of samples from patients with hairy cell leukemia.