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

Summary 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.