The prognostic significance of <scp>del6q23</scp> in chronic lymphocytic leukemia
Authors: Hadiyah Y. Audil, Paul J. Hampel, Daniel L. Van Dyke, Sara J. Achenbach, Kari G. Rabe, Stephanie A. Smoley, Timothy G. Call, Wei Ding, Min Shi, Curtis A. Hanson, Yucai Wang, Eli Muchtar, Amber B. Koehler, Susan M. Schwager, Jose F. Leis, Esteban Braggio, Susan L. Slager, Neil E. Kay, Saad S. Kenderian, Sameer A. Parikh
Journal: American Journal of Hematology (2021)

The clinical course of patients with newly-diagnosed chronic lymphocytic leukemia (CLL) is heterogeneous – an estimated 30% of patients never require treatment on long-term follow-up; on the other hand, a significant number of patients need therapy in the first few years after diagnosis.1 The Dohner classification is the gold standard for cytogenetics-based risk stratification, and uses fluorescence in situ hybridization (FISH) to identify chromosomal abnormalities commonly associated with CLL, including del17p13, del13q14, del11q22, and trisomy 12.1 Other less-common cytogenetic aberrations have also been noted, including deletion of 6q in 3–7% of CLL cases.1, 2 The prognostic significance of del6q23 remains controversial, likely due to its uncommon occurrence compared to the four other more routinely-noted FISH defects. Several studies have suggested an association of del6q23 with inferior outcomes including shorter overall survival (OS) and shorter treatment-free interval, although others have shown no difference in outcomes.2, 3 These studies are limited by small sample sizes, inclusion of both previously untreated and treated CLL patients, and lack of adequate accounting of other confounding factors. In this study, we comprehensively characterized clinical and cytogenetic profiles and outcomes in previously untreated CLL patients with del6q23 seen at Mayo Clinic over the past 25 years. The Mayo Clinic CLL Database is comprised of CLL patients seen in the Division of Hematology at Mayo Clinic, Rochester, MN since 1995 who have granted permission for their records to be used for research. Clinical characteristics including age, sex, Rai stage, CD38 expression, ZAP70, CD49d, immunoglobulin heavy chain gene (IGHV) mutation status, and FISH findings of previously untreated CLL patients with del6q23 were compared to patients without del6q23. We also computed the CLL-International Prognostic score (CLL-IPI) for all patients where this information was available. FISH was performed on cell suspensions using standard techniques. This study was approved by the Mayo Clinic Institutional Review Board. Time to first therapy (TTFT) was defined as time from FISH to initiation of treatment or last known date when the patient was not treated. Patients treated on an early intervention clinical trial protocol were censored for TTFT analysis on the date of receipt of treatment. Cumulative incidence of TTFT was adjusted for competing risk of death. Overall survival was defined as time from FISH to date of death due to any reason. Gray's test was used to test for differences in the presence of del6q23 for TTFT, and the log-rank test was used for OS. We also analyzed TTFT and OS among patients with del6q23 categorized as follows: (a) del6q23 as the sole abnormality; (b) del6q23 with low-risk Dohner FISH (del13q14); and (c) del6q23 with high-risk Dohner FISH (del11q23 and del17p13). The proportion of del6q23 patients who would drop out of comprehensive multivariable analyses due to incomplete prognostic marker data, caused concern that results would not be representative; therefore, we performed a case–control study to analyze the independent effect of del6q23 on outcomes. For each CLL patient with del6q23 (case), we identified four CLL patients without del6q23 (controls) matched by CLL-IPI risk group and sex, and analyzed TTFT and OS between the two groups. All analyses were conducted in SAS 9.4. We identified 3101 previously untreated CLL patients, of whom 42 (1.4%) had del6q23. The mean percentage of abnormal nuclei was 36.9 ± 25.2 (median 29.0, range 7.5–91.5). The baseline characteristics of all patients are shown in Table S1. When compared to patients without del6q23, patients with del6q23 were enriched for more adverse risk markers including advanced Rai stage III–IV (22% vs. 9%, p = .002), unmutated IGHV genes (91% vs. 43%, p < .001), beta-2-microglobulin (3.0 μg/mL vs. 2.5 μg/mL, p = .005), and high and very high risk CLL-IPI score (50% vs. 27%, p < .001). Of the 42 patients with del6q23 at diagnosis, 13 patients (31%) had a sole del6q23; of the remaining patients, del6q23 co-occurred with del13q14 in eight patients (19%), with del11q22 in 13 patients (31%) and with del17p13 in eight patients (19%). Detailed FISH findings can be found in Table S2. Twenty-nine patients received CLL therapy, and two additional patients were treated in a clinical trial for early intervention in high-risk CLL. Median OS was 6.0 years in patients treated with chemoimmunotherapy or chemotherapy alone and 5.3 years in patients treated with monoclonal antibody therapy; all patients treated with BTK inhibitors were alive at last follow-up date (p = .47; Figure S1). The median follow-up of all patients was 7.3 years. Patients with del6q23 had a significantly shorter median TTFT compared to patients without del6q23 (0.7 vs. 6.1 years, p < .001; Figure 1(A)). Patients with del6q23 had a significantly shorter OS compared to patients without del6q23 (10.9 years vs. 13.1 years, p = .044; Figure 1(B)). Figures S2A and B show TTFT and OS, respectively, according to individual FISH findings compared to patients with del6q23. Among patients with del6q23 (n = 42), the median TTFT with sole del6q23 (n = 13), del6q23 with low-risk Dohner FISH (n = 8), and del6q23 with high-risk Dohner FISH (n = 21) was 1.0 versus 1.7 versus 0.4 years, respectively (p = .28; Figure 1(C)). The corresponding median OS for these three groups was 10.9 years, not reached, and 6.1 years, respectively (p = .15; Figure 1(D)). Table S3 shows the characteristics of CLL patients with del6q23 (cases, n = 42) compared to those without del6q23 (controls, n = 168; 1:4 ratio) matched according to CLL-IPI score and sex. Figure 1(E) shows that the median TTFT was shorter among patients with del6q23 compared to matched controls without del6q23 (0.7 vs. 3.9 years, p = .07), although this did not meet the threshold of statistical significance. Figure 1(F) shows there was no significant difference in median OS among patients with del6q23 compared to matched controls without del6q23 (10.9 vs. 10.3 years respectively, p = .28). The major findings of our study are as follows – (a) del6q23 is a rare abnormality in previously untreated CLL patients, present in 1 of ~80 newly-diagnosed CLL patients in our cohort; (b) patients with del6q23 are enriched for other high-risk markers such as unmutated IGHV genes (91%), and del11q23 or del17p13 by FISH (50%); and (c) although TTFT and OS are significantly shorter in patients with del6q23 compared to those without del6q23, these differences are likely due to other concomitant high-risk features. It is worth noting that the incidence of del6q23 in our cohort (1.4%) is substantially lower than the previously-published incidence of 3–7%; this is likely due, in part, to the fact that we defined incidence as the presence of del6q23 at or near diagnosis, and did not include the presence of del6q23 acquired later in the disease course as has been done in other studies. The use of del6q in risk stratification of CLL is limited in part by heterogeneity of existing literature regarding the extent of chromosome 6 evaluation. Since 2002, the Mayo CLL FISH panel includes a probe specifically for 6q23.3. Other studies have used cohorts comprised of patients with del6q identified using single probes for 6q (6q21, 6q23) or multiple probes for 6q (6q21 and 6q27; 6q16, 6q23, 6q25, and 6q27), with Jarosova et al. mapping the extent of del6q present in each patient using array comparative genomic hybridization.2-4 The biologic basis of del6q23.3 possibly rests in the disruption of the tumor necrosis factor alpha-induced protein 3 (TNFAIP3) gene, which normally encodes for the NF-κB inhibitor A20.5 Interestingly, from an etiologic standpoint, A20 has also been identified as a tumor suppressor protein in Hodgkin lymphoma, several subtypes of non-Hodgkin lymphomas (including mantle cell lymphoma and diffuse large B-cell lymphoma), and primary mediastinal B-cell lymphoma, further supporting its potential role in the pathogenesis of lymphocytic malignancies when downregulated.5 The prognostic significance of del6q been studied more widely in other malignancies. In particular, del6q has been established as a marker of poor prognosis in Waldenstrom macroglobulinemia and other monoclonal gammopathies, and as a marker of intermediate prognosis in acute lymphocytic leukemia.2, 6 The presence of del6q has also been reported in several solid tumors (including cancers of the salivary gland, breast, bladder, ovaries, pancreas, and prostate), although its prognostic impact in these settings is less defined.6 Results from our study are congruent with published studies in the literature and show that the presence of del6q23 is associated with a shorter TTFT and OS compared to patients without del6q23. By using a case–control approach matching each patient with del6q23 to four patients without del6q23, we show that patients with del6q23 have a shorter TTFT, although the P value did not cross the threshold of statistical significance. There was no difference in OS between the two groups of patients. It is plausible that the presence of del6q23 represents additional genomic instability. This latter biologic phenomenon may be captured by performing other tests such as CpG stimulated karyotype or using next generation sequencing. Unfortunately, these were not performed on our patients in this retrospective study; prospective studies will be needed to better understand this. In summary, the findings of our study confirm that del6q23 in treatment-naïve CLL represents an uncommon abnormality. We also affirm that CLL patients with del6q23 have a more adverse clinical and cytogenetic profile, which is reflected by a shorter treatment-free survival. Results of this study were presented in part at the 25th European Hematology Association Congress held virtually in June 2020. The conduct of this research was supported in part by the Henry J. Predolin Foundation. Sameer A. Parikh and Saad S. Kenderian also acknowledge support from the Mayo Clinic K2R Career Development Program. S.A.P.: Research funding has been provided to the institution from Pharmacyclics, Janssen, AstraZeneca, TG Therapeutics, Merck, AbbVie, and Ascentage Pharma for clinical studies in which S.A.P. is a principal investigator. He has also participated in advisory board meetings of Pharmacyclics, AstraZeneca, Genentech, GlaxoSmithKline, Innate Pharma, and AbbVie (he was not personally compensated for his participation). N.E.K.: Research funding from: Acerta Pharm, Pharmacyclics, MEI Pharma, and Tolero. He is on a data safety monitoring committee for: Agios Pharm, Celgene, Sunesis, Cytomx Therapeutics, Morpho-Sys, Rigel Pharm and Juno Therapeutics. He is on an advisory Board for Astra Zeneca, Cytomx Therapeutics, Pharmacyclics Dava Oncology, Acerta Pharma BV, and Juno Therapeutics. S.S.K.: S.S.K. is an inventor on patents in the field of CAR immunotherapy that are licensed to Novartis (through an agreement between Mayo Clinic, University of Pennsylvania, and Novartis), Humanigen (through Mayo Clinic), Morphosys (through Mayo Clinic), Tolero (through Mayo Clinic), and Mettaforge (through Mayo Clinic). S.S.K. receives research funding from Kite, Gilead, Juno, Celgene, Novartis, Humanigen, MorphoSys, Tolero, Sunesis, Leahlabs and Lentigen. S.S.K. has participated in consultancy with Torque, Leahlabs, and Kiniksa. S.S.K. has participated in scientific advisory board meetings of Juno, Kite, and Humanigen, and data safety monitoring board meetings of Humanigen. W.D.: Research funding from Merck and DTRM. Advisory board: Merck and Octapharma (no personal compensation). Y.W.: Research funding (to the institution) from Incyte, InnoCare, Norvatis, and Genentech. E.B.: E.B. is a consultant of DASA. All other authors declare no competing financial interests. Figure S1. Overall survival in CLL patients with de16q23, according to first line treatment administered. First-line treatment consisted of chemoimmunotherapy or chemotherapy alone in 16 patients (52%), Bruton tyrosine kinase inhibitor (BTK) inhibitor in 7 patients (23%), anti-CD20 monoclonal antibody alone in 6 patients (19%), and rituximab/alemtuzumab in 2 patients (both these patients were treated on the early intervention study protocol; 6%). Figure S2. (A) Time to first therapy in all patients according to individual FISH findings, compared to patients with del6q23 on FISH. (B) Overall survival in all patients according to individual FISH findings, compared to patients with del6q23 on FISH. Table S1. Baseline characteristics of all patients Table S2. Concomitant FISH abnormalities in previously untreated patients with del6q23 (n = 42) Table S3. Baseline characteristics of CLL patients with del6q23 compared to CLL patients without del6q23, matched for sex and CLL-IPI risk score Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.