Tumor markers in hairy cell leukemia.

Despite the availability of highly effective therapies for hairy cell leukemia, including cladrabine, deoxycoformycin, and interferon α, a significant fraction of patients relapse. The use of flow cytometry, bone marrow examination for minimal residual disease, and peripheral blood counts provides details about the level of disease activity, but the optimal method for following patient response and risk for relapse has not been established. Flow cytometry provides accurate assessments of circulating malignant cell counts even at very low levels, but does not provide details on the extent of bone marrow involvement. Bone marrow involvement can be assessed by biopsy, but is a painful procedure, and the extent of involvement by hairy cell leukemia is not always uniform. Thus, a single biopsy may not identify active disease when it is present. Magnetic resonance imaging is being evaluated as a means for assessing total body burden of disease in the marrow and shows great promise. Tumor markers that can be measured in the serum provide a method for assessing total body disease burden. Cell surface proteins can be shed by tumor cells through proteolytic cleavage to release portions of their extracellular domains. These proteolytic degradation products can be measured in the serum and provide a tool to monitor disease burden and response to therapy. Three cell surface molecules expressed by the malignant hairy cells, CD25, CD22, and CD307, have been used to monitor disease activity and follow patients at risk for relapse. Serum tumor markers provide a reliable, inexpensive, and non-invasive means of following patients with hairy cell leukemia for response to treatment and relapse.