Serum FLCs prior to treatment and on ibrutinib. Box and whisker plots (10th-90th percentile) of (A) serum κ:λ ratio, (B) κ FLC, and (C) λ FLC in κ-clonal CLL (n = 39). Box-and-whisker plots (10th-90th percentile) of (D) serum κ:λ ratio, (E) κ FLC, and (F) λ FLC in λ-clonal CLL (n = 28). Only paired data are shown. Y-axis is in log2 scale. Dotted lines illustrate the normal range. Statistical significance is indicated by *P < .05, **P < .01, ***P < .001, ****P < .0001, or ns (P ≥ .05) compared with pretreatment baseline.