Hairy cell leukemia-related disorders consistently show low CD27 expression.

In Japan, typical hairy cell leukemia (HCL) is rare, and HCL-Japanese variant (HCL-JV) is more common. Hairy B-cell lymphoproliferative disorder (HBLD) is another unusual disorder of polyclonal B-lymphocytosis of hairy cell appearance. In the present study, we analyzed the clinical features of 3 patients with HCL, 3 with HCL-JV, and 3 with HBLD. All HBLD patients had the DRB1*04 allele. As compared with other B-cell lymphoproliferative disorders, CD27 expression on B cells was significantly lower in all patients, ranging from 0.3% to 23.4%. Our results suggest that low CD27 expression may be a distinct feature of these HCL-related disorders.