CD49d Expression Is Included in a Revised 4-Factor Model Predicting Outcome in Patients with Chronic Lymphocytic Leukemia Treated with Ibrutinib: A Multi-Center Real-World Experience

Introduction. Expression of the CD49d integrin chain has prognostic impact on ibrutinib (IB)-treated CLL patients (Tissino et al, J Exp Med, 2018; Tissino et al, Blood 2020). In addition, a 4-factor (4-f) score, based on TP53 aberration, β2-microglobulin (β2M), lactate dehydrogenase (LDH) and previous therapy lines was proposed to identify patients at a higher risk of treatment failure or death during IB therapy (Ahn et al, J Clin Oncol, 2020; Morabito et al, Am J Hematol, 2021). The clinical impact of TP53 disruption was recently refined by demonstrating that only the co-presence of TP53 deletion and mutations, and not the single aberrations, has prognostic value in the IB setting (Bomben et al, Leukemia 2022). The aim here is to integrate these observations in a comprehensive scoring for the management of IB-treated patients.

Methods. This study is a retrospective/multicenter analysis of 410 CLL patients treated with IB in the current clinical practice (December/2013-March/2021). Outcome data were updated as of March/2023. Median follow-up from IB treatment was 29.5 months (95% CI 26.7-33.1 months); 57 patients were treatment naïve (0 previous lines), while 353 had ≥1 previous lines. CLL patients were characterized for CD49d expression and for the 4-f variables, TP53 disruption was evaluated by FISH and TP53 mutational status by NGS (low-VAF mutations included). OS or PFS were measured from the date of IB treatment to the date of death (OS), or progression/death (PFS) or last follow-up.

Results. 1) The canonical 4-f was applied as previously described, identifying 111 low-, 163 intermediate (int)-, and 136 high-risk patients. Patients in the low-risk group had a longer OS than patients in the int-, and high-risk groups (P=0.0115 and P=0.0011), while no difference was found comparing patients in the int- vs. high-risk groups (P=0.3036). 2) We generated a modified version of the 4-f score by considering: i) as TP53 disrupted only patients presenting a concomitant TP53 deletion and mutation (n=93); ii) since no difference in terms of OS was found comparing previously untreated patients (n=57) and patients treated with 1 previous line (n=157; P=0.78), these two groups were combined (n=214) and kept separated from patients who had received >1 previous lines of therapy (n=196). Accordingly, the 4-f-modified identified 218 low-, 109 int-, and 83 high-risk patients, the 3 groups presented different OS, the latter model outperforming the canonical 4-f score (C-indices 0.616 vs 0.639; P<0.0001). 3) CD49d-high CLL cases (i.e. CLL with CD49d expression ≥30% and/or with CD49d-bimodal expression; n=268) had shorter OS and PFS intervals (P=0.0005 and 0.0194, respectively) than CD49d-low cases (n=142). By combining these observations, CD49d remained an independent prognostic factor for OS (P=0.004) in a multivariable model, which included the 4-f-modified int-risk (P=0.0585) and high-risk (P=0.0011) groups. Driven by these findings, we re-analyzed the single parameters of the 4-f score along with CD49d expression. According to a new multivariable analysis (Fig. A), LDH was not included in the final model, which in turn included CD49d expression as independent OS predictor (P=0.0011). 4) We then redesigned a novel 4-f model excluding LDH data in favor of CD49d expression data (4-factor-CD49d). Each of the four factors contributed one point and stratified patients (n=407/410) into three groups with a significantly different risk for OS probability, merged on a one-to-one risk group comparison basis: score 0-1, low-risk (n=185); score 2-3, int-risk (n=211); score 4, high-risk (n=11; Fig. B). The inclusion of CD49d into this novel 4-f model improved its prediction capability (C-index=0.663; P<0.0001 versus both the original 4-f and the 4-f-modified). Similar results were obtained when considering PFS as clinical readout.

Conclusions. Evidence is provided that in the context of CLL patients treated with IB in a real-world setting, variables like B2M, the number of previous lines of therapy and assessment of TP53 disruption remain important tools for identifying patients at a higher risk of relapse/death. Here we emphasize the need of a comprehensive assessment of TP53 aberrations considering TP53 deletions and mutations simultaneously, and propose to add the assessment CD49d expression, integrating these four variables into a novel 4-f-CD49d scoring system. Further validation in independent cohorts is needed.