Telomere Length and CD49d Cooperate with IGHV Gene Status As Predictors of Long-Term Progression-Free Survival in CLL Patients Treated with FCR-Based Regimens

▪ Background - Although there has been a revolution in the treatment of chronic lymphocytic leukemia (CLL), the challenge remains to identify the right drugs for the right patients. It is widely accepted that CIT, including the ‘gold standard’ fludarabine, cyclophosphamide and rituximab (FCR), is contraindicated for patients with TP53 disruption and, more recently, unmutated IGHV genes. Also patients with short, dysfunctional telomeres were shown to have inferior outcomes when treated with FCR-based regimens. To date, a role for CD49d in this setting has not been established. Aims - Here we evaluated the ability of telomere lenght (TL) and CD49d to cooperate with IGHV gene status to predict progression-free survival (PFS) in patients treated with FCR-based regimens in the frontline setting in three UK trials, ARCTIC, ADMIRE and CLL4. Methods - The study included a discovery cohort of 245 CLL treated with FCR/FCR-like regimens according to the two UK trials ARCTIC and ADMIRE. As there was no significant difference in PFS between the three arms of the study (P = 0.97), analysis was performed on the combined cohort. The median follow-up was 77.5 months with 157 progressions and 76 deaths. Twenty-nine patients were TP53 deleted and/or mutated, with shorter PFS compared to cases without TP53 disruption (final cohort, 216 TP53 wild-type CLL). The validation cohort was composed of 119 CLL samples derived from patients randomised to receive fludarabine, cyclophosphamide (FC) from the UK CLL4 trial. The median follow-up was 67.2 months with 99 progressions and 77 deaths. Fifteen CLL were TP53 mutated/deleted, with shorter PFS compared to cases without TP53 disruption (final cohort, 104 TP53 wild-type CLL). TL was measured using the high-throughput STELA assay and patients were bifurcated into two groups with either short telomeres inside the fusogenic range (TL-IFR) or long telomeres outside the fusogenic range (TL-OFR). CD49d was measured by flow cytometry and dichotomized as CD49dpos and CD49dneg based on the established 30% cut-off. For IGHV gene status, the 2% cutoff was used to split patients in mutated (IGHV-M) and ummutated (IGHV-UM). Results - In the 216 CLL with wild-type TP53 status from the ARCTIC/ADMIRE trials, CD49d expression was a predictor of PFS (P=0.02; HR=1.46 [1.03-2.06]). In keeping with previous reports, patients with IGHV-UM genes (P