Soluble interleukin-2 receptor in hairy-cell leukemia: a reliable marker of disease

The CD25 molecule, which corresponds to the p55 alpha chain of the interleukin-2 receptor, is strongly expressed by neoplastic cells in hairy-cell leukemia and is released in large amounts in the soluble form which is detectable in serum. In order to assess the reliability of the soluble interleukin-2 receptor as a disease marker in the management of patients with hairy-cell leukemia, we investigated serum levels in 35 untreated patients and in 2 patients with the hairy-cell leukemia variant. In 21 of 35 patients soluble receptor levels were also monitored during and after recombinant interferon-alpha therapy. Clinical and hematological parameters were also assessed. Soluble interleukin-2 receptor levels were extremely high at the time of diagnosis in patients with typical hairy-cell leukemia [32,722 +/- 27,001 vs. 331 +/- 145 units/ml in controls (mean +/- SD)], but not in patients with the leukemia variant. A progressive decrease in soluble interleukin-2 receptor levels paralleled the clinical response to treatment, although normal values were never detected, even in patients who achieved an apparent complete remission. After recombinant interferon-alpha discontinuation, disease recurrence was accompanied by a progressive increase to pre-treatment soluble receptor levels. Overall, a close correlation was found between soluble interleukin-2 receptor values and total tumor burden (r = 0.84, P < 0.001). On the basis of these data, soluble interleukin-2 receptor should be regarded as a key marker in the management of patients with hairy-cell leukemia.