MARROW MAST-CELL HYPERPLASIA IN HAIRY-CELL LEUKEMIA

Marrow mast cells, frequently elevated in chronic B-lymphoproliferativ e disorders, were counted per high magnification field (HMF) on toluid ine blue stained marrow biopsies from 34 patients diagnosed with hairy cell leukemia (HCL); similar counts were performed on splenic section s from nine of these patients. Biopsies from 28 normal marrow transpla nt donors and 10 normal spleens served as controls. Mast cells were di stributed irregularly throughout normal and HCL marrows, but tended to be more concentrated about the hairy cells in cases focally involved by HCL. HCL marrows averaged 12.7 mast cells/HMF compared to 1.1 for c ontrols. Although most normal marrows (86%) averaged < 2 mast cells/HM F, 88% of HCL cases averaged greater than or equal to 2 mast cells/HMF . Splenic mast cells averaged < 1/HMF for both HCL and control cases. By electron microscopy, marrow mast cells in HCL demonstrated normal s ubstructure with numerous granules. The cell surfaces of mast cells sh owed filopodia that often came in contact with those of hairy cells. T hese results indicate most HCL marrows, but not spleens, are associate d with varying degrees of mast cell hyperplasia. Furthermore, this stu dy suggests a biologic interaction between mast cells and hairy cells. The significance of marrow mast cell hyperplasia in HCL is unknown, b ut these mast cells may contribute to the increased reticulin fiber ne twork observed in HCL marrows.