Serum soluble interleukin-2 receptor levels in hairy cell leukaemia as a marker of tumour burden with prognostic value and as a tool for disease monitoring.

Leukaemic cells from hairy cell leukaemia (HCL) secrete a soluble form of the interleukin-2 receptor (sIL-2R) which is measurable in serum. Previous evidence suggested that sIL-2R may correlate well with tumour burden and demonstrated a reduction in sIL-2R levels after therapy with recombinant interferon-α2. We evaluated the role of sIL-2R as a new prognostic factor and as a tool for disease monitoring. sIL-2R correlated well with other markers of neoplastic bulk and markedly decreased after treatment, with lower levels achieved in patients reaching complete remission (p = 0.002) or negative minimal residual disease (MRD, p = 0.034). Post-treatment levels ≤827 kU/L were strongly predictive of longer time to next treatment (TTNT) (median NR vs. 4.87 years; hazard ratio [HR]: 0.10; 95% confidence interval [CI]: 0.02-0.24; p < 0.001) and higher 5- and 10-year TTNT rates (5-year: 93% vs. 45%; 10-year: 83% vs. 11%). Furthermore, a ≥50% increase in sIL-2R levels over any 1-year interval during follow-up predicted impending relapse. In a context where patients with HCL are expected to achieve a life expectancy comparable to that of the general population, sIL-2R has the potential to serve as a non-invasive tool alongside MRD to predict relapse and to identify those patients who may fail to derive the most benefit from current treatments.