Serum levels of soluble interleukin‐2 receptor in hairy cell leukaemia: a reliable marker of neoplastic bulk

In hairy cell leukaemia (HCL), the strong membrane expression of the Tac antigen, corresponding to the p55 chain of the interleukin‐2 receptor (IL‐2R), is associated with the presence in the serum of high levels of a soluble form of the same molecule (sIL‐2R). Previous observations that therapy‐induced clinical and haematologic improvement in HCL is accompanied by a progressive decrease of sIL‐2R suggest a possible correlation between sIL‐2R levels and tumour burden. To verify this hypothesis, we monitored the variation of sIL‐2R values in 13 non‐splenectomized HCL patients admitted for treatment with recombinant interferon alpha‐2. The data were correlated with the estimated weight of bone marrow (BM) and spleen infiltrations, which in these patients almost entirely account for the tumour mass. The regression analysis test showed a direct correlation between sIL‐2R values and both BM neoplastic involvement (r= 0.63) and spleen tumour mass (r= 0.76). In addition, the correlation was further improved (r= 0.86) when sIL‐2R values were correlated with the total neoplastic mass, as calculated by the sum of spleen and BM neoplastic tissue weight. These data indicate that the detection of sIL‐2R in HCL is a reliable non‐invasive marker of tumour burden, which can be regarded as an additional useful tool for monitoring treatment response.