Serum level of CD26 predicts time to first treatment in early B-chronic lymphocytic leukemia

We analyzed the correlation between well-established biological parameters of prognostic relevance in B-cell chronic lymphocytic leukemia (CLL) [i.e. mutational status of the immunoglobulin heavy chain variable region (IgV(H)), ZAP-70- and CD38-expression] and serum levels of CD26 (dipeptidyl peptidase IV, DPP IV) by evaluating the impact of these variables on the time to first treatment (TFT) in a series of 69 previously untreated Binet stage A B-cell CLL patients. By using a commercial ELISA we found that with exception of a borderline significance for ZAP-70 (P = 0.07) and CD38 (P = 0.08), circulating levels of CD26 did not correlate with either Rai substages (P = 0.520) or other biomarker [beta2-microglobulin (P = 0.933), LDH (P = 0.101), mutational status of IgV(H) (P = 0.320)]. Maximally selected log-rank statistic plots identified a CD26 serum concentration of 371 ng/mL as the best cut-off. This threshold allowed the identification of two subsets of patients with CD26 serum levels higher and lower that 371 ng/mL respectively, whose clinical outcome was different with respect to TFT (i.e. 46% and 71% at 5 yr respectively; P = 0.005). Along with higher serum levels of CD26, the univariate Cox proportional hazard model identified absence of mutation in IgV(H) (P < 0.0001) as predictor of shorter TFT. As in multivariate analysis all these parameters maintained their discriminating power (mutational status of IgV(H,)P < 0.0001; soluble CD26, P = 0.02) their combined effect on clinical outcome was assessed. When three groups were considered: (1) Low-risk group (n = 31), patients with concordant IgVH(mut) and low level of soluble CD26; (2) intermediate risk group (n = 26), patients with discordant pattern; (3) high-risk group (n = 12), patients with concordant IgVH(unmut) and high level of soluble CD26, differences in the TFT were statistically significant, with a TFT at 5 yr of respectively 88%, 51% and 43% (P < 0.0001). Our results indicate that in early B-cell CLL biological profile including among other parameters soluble CD26 may provide a useful insight into the complex interrelationship of prognostic variables. Furthermore, CD26 along with mutational status of IgV(H) can be adequately used to predict clinical behavior of patients with low risk disease.