Classic hairy cell leukemia (HCL) is a B-cell malignancy with distinctive immunophenotype, typically having BRAF V600E mutation, and expressing CD20, CD22, CD25, CD11c, CD103, CD123, annexin A1 (Anxa1), and tartrate-resistant acid phosphatase (TRAP) [1–4]. This evidence concerns the gene CD22 and hairy cell leukemia.