Immunoglobulin light chain mutational status refines IGHV prognostic value in identifying chronic lymphocytic leukemia patients with early treatment requirement

The mutational status of immunoglobulin (IG) light chain genes in chronic lymphocytic leukemia (CLL) and its clinical impact have not been extensively studied. To assess their prognostic significance, the IG light chain gene repertoire in CLL patients has been evaluated using a training-validation approach. In the training cohort (N = 573 CLL), 92.5% showed productive IG light chain genes rearrangements, with IGKV4-1 (20.5%) and IGLV3-21 (19.0%) being the most common. A 99.0% somatic hypermutation cut-off was identified as the best predictor for time to first treatment (TTFT) in 414 Binet A CLL patients of the training cohort. Patients with unmutated (UM) light chain genes displayed a 10-year treatment free probability of 32.4% versus 73.2% for those with mutated (M) genes (p < 0.0001). Importantly, UM light chain genes maintained an independent association with a shorter TTFT when adjusted for the IPS-E prognostic model variables, that also includes IGHV mutational status. The validation cohort of 343 Rai 0 patients confirmed these findings, with UM light chain genes predicting a 7-year treatment free probability of 42.0% versus 73.7% for M genes (p < 0.0001). These results indicate that the mutational status of the light chain genes is an independent predictor of shorter TTFT in early-stage CLL patients.