Hairy cell leukemia (leukemic reticuloendotheliosis) in serous effusions

The cytology of two cases of hairy cell leukemia (leukemic reticuloendotheliosis) involving pleural and ascitic fluids is described. With the Papanicolaou stain, the cells have a "lymphoid" appearance. The presence of these cells plus knowledge of the clinical history might help the cytologist and/or hematologist in their identification. A tartrate resistant acid phosphatase (TRAP) stain will confirm the true nature of such cells and establish the clinical diagnosis of hairy cell leukemia. Unlike the other members of the leukemia-malignant lymphoma group, the body cavities are rarely involved.