The kappa/lambda ratio of surface immunoglobulin light chain as a valuable parameter for MRD assessment in CLL with atypical immunophenotype.

In recent years, the significance of detecting minimal/measurable residual disease (MRD) in chronic lymphocytic leukemia (CLL) has increased due to the availability of highly effective therapeutic agents. Flow cytometry provides notable cost-effectiveness and immediacy, with an expected sensitivity level of approximately 10-4. The critical aspect of MRD detection via flow cytometry lies in accurately defining the region containing tumor cells. However, a subset of CLL, known as CLL with atypical immunophenotype, exhibits a distinct cell surface marker expression pattern that can make MRD detection challenging, because these markers often resemble those of normal B cells. To enhance the sensitivity of MRD detection in such atypical cases of CLL, we have capitalized on the observation that cell surface immunoglobulin (sIg) light chains tend to be expressed at a higher level in this subtype. For every four two-dimensional plots of cell surface markers, we used a plot to evaluate the expression of sIg kappa/lambda light chains and identified regions where the kappa/lambda ratio of sIg light chains deviated from a designated threshold within the putative CLL cell region. Using this method, we could detect atypical CLL cells at a level of 10-4. We propose this method as an effective MRD assay.

Performance of a novel eight-color flow cytometry panel for measurable residual disease assessment of chronic lymphocytic leukemia.

BACKGROUND: Measurable residual disease (MRD) is an important prognostic indicator of chronic lymphocytic leukemia (CLL). Different flow cytometric panels have been developed for the MRD assessment of CLL in Western countries; however, the application of these panels in China remains largely unexplored. METHODS: Owing to the requirements for high accuracy, reproducibility, and comparability of MRD assessment in China, we investigated the performance of a flow cytometric approach (CD45-ROR1 panel) to assess MRD in patients with CLL. The European Research Initiative on CLL (ERIC) eight-color panel was used as the "gold standard." RESULTS: The sensitivity, specificity, and concordance rate of the CD45-ROR1 panel in the MRD assessment of CLL were 100% (87/87), 88.5% (23/26), and 97.3% (110/113), respectively. Two of the three inconsistent samples were further verified using next-generation sequencing. In addition, the MRD results obtained from the CD45-ROR1 panel were positively associated with the ERIC eight-color panel results for MRD assessment (R = 0.98, p < 0.0001). MRD detection at low levels (≤1.0%) demonstrated a smaller difference between the two methods (bias, -0.11; 95% CI, -0.90 to 0.68) than that at high levels (>1%). In the reproducibility assessment, the bias was smaller at three data points (within 24, 48, and 72 h) in the CD45-ROR1 panel than in the ERIC eight-color panel. Moreover, MRD levels detected using the CD45-ROR1 panel for the same samples from different laboratories showed a strong statistical correlation (R = 0.99, p < 0.0001) with trivial interlaboratory variation (bias, 0.135; 95% CI, -0.439 to 0.709). In addition, the positivity rate of MRD in the bone marrow samples was higher than that in the peripheral blood samples. CONCLUSIONS: Collectively, this study demonstrated that the CD45-ROR1 panel is a reliable method for MRD assessment of CLL with high sensitivity, reproducibility, and reliability.

Ibrutinib discontinuation and associated factors in a real-world national sample of elderly Medicare beneficiaries with chronic lymphocytic leukemia.

Prior studies evaluating ibrutinib discontinuation are limited to clinical trials and selected medical centers and hence may not reflect real-world practice. This study used Medicare claims (2013-2019) to examine ibrutinib discontinuation and associated factors among elderly patients with chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL). Over a median follow-up of 2.1 years, two-thirds (65.2%) of the 11,870 new ibrutinib initiators were discontinued, with half (45.1%) of patients discontinuing within 12 months of initiation. Factors such as advanced age, lack of Part D low-income subsidy, evidence of prior CLL/SLL treatment, and cardiovascular comorbidities (e.g. atrial fibrillation) were associated with higher risk of discontinuation. Over a median of 1.2 years from discontinuation, 40% of discontinuers initiated another CLL/SLL treatment after ibrutinib discontinuation; 25% of patients restarted ibrutinib treatment at some point over follow-up. Our findings point to a large unmet need with the widely used BTKi ibrutinib and underscore the importance of ongoing development of efficacious and well-tolerated CLL/SLL therapies.

Real-world adherence and discontinuation among Medicare beneficiaries initiating venetoclax vs. BTKis in relapsed/refractory chronic lymphocytic leukemia.

The treatment landscape for chronic lymphocytic leukemia (CLL) has been transformed by the availability of Bruton's tyrosine kinase inhibitors (BTKis) and the B-cell lymphoma 2 (BCL-2) inhibitor venetoclax. Despite clinical trial data supporting these novel oral agents, evidence evaluating real-world adherence is limited. This study used 2015-2019 Medicare claims data for elderly patients with relapsed/refractory CLL to assess differences in real-world adherence and discontinuation in the 12 months after treatment initiation. In the final sample of 711 venetoclax patients and 1,566 BTKi patients, we found that those initiating venetoclax tended to be younger (mean age 75.6 [SD 6.0] vs 77.6 [SD 6.9] years, p < .001) but had poorer clinical characteristics. After risk-adjustment, the venetoclax group had higher adherence (61.9% vs. 45.4%, p < .0001) and lower discontinuation when compared to the BTKi group (28.5% vs. 47.4%, p < .001). These favorable real-world findings underscore the importance of developing well-tolerated novel combinations for older adults.

Assessment of rituximab-abbs, a biosimilar, and rituximab outcomes in patients with CLL or NHL: A real-world UK study.

BACKGROUND: Rituximab (chimeric anti-CD20 monoclonal antibody) treatment is approved for chronic lymphocytic leukemia (CLL) and non-Hodgkin lymphoma (NHL). Rituximab-abbs (first biosimilar approved in 2017) is expected to significantly reduce healthcare economic burden due to lower acquisition costs. This non-interventional, non-comparative study assessed real-world effectiveness and tolerability of rituximab-abbs and rituximab in treatment-naive patients with CLL or NHL. MATERIALS AND METHODS: Via an online physician survey, 46 UK-registered hematologists and oncologists retrospectively reported on randomly selected patients aged ≥18 years with CLL or NHL with rituximab-abbs or rituximab as first-line immunotherapy. Overall, 201 patient charts were examined across 4 cohorts: rituximab-abbs in CLL, rituximab-abbs in NHL, rituximab in CLL, rituximab in NHL. RESULTS: Demographic profiles across cohorts were similar. Most patients (94 %-100 %) received combination therapy (rituximab-abbs or rituximab mainly with chemotherapy). For both treatments, overall response rate (94 %-98 %) and 1-year overall survival (98 %-100 %) were very high for patients with CLL or NHL. Most common serious adverse events were neutropenia, fatigue, anemia and infusion reactions. The majority of patients (54 %-66 %) did not experience a grade ≥3 adverse event. Healthcare resource utilization was similarly high across cohorts, driven by diagnostic testing, oncologist office visits, and day-case hospital admissions; many patients required supportive medical therapies. Mean annual savings of ∼£1000/patient driven by acquisition costs occurred with rituximab-abbs versus rituximab, administration costs were similar. CONCLUSION: Rituximab-abbs and rituximab demonstrated similar effectiveness and tolerability in treating CLL and NHL in routine UK clinical practice and demonstrate the utility of the biosimilar as a cost-saving alternative treatment.

Prognostic value of high-sensitivity measurable residual disease assessment after front-line chemoimmunotherapy in chronic lymphocytic leukemia.

Measurable residual disease (MRD) status is widely adopted in clinical trials in patients with chronic lymphocytic leukemia (CLL). Findings from FILO group trials (CLL2007FMP, CLL2007SA, CLL2010FMP) enabled investigation of the prognostic value of high-sensitivity (0.7 × 10-5) MRD assessment using flow cytometry, in blood (N = 401) and bone marrow (N = 339), after fludarabine, cyclophosphamide, and rituximab (FCR)-based chemoimmunotherapy in a homogeneous population with long follow-up (median 49.5 months). Addition of low-level positive MRD < 0.01% to MRD ≥ 0.01% increased the proportion of cases with positive MRD in blood by 39% and in bone marrow by 27%. Compared to low-level positive MRD < 0.01%, undetectable MRD was associated with significantly longer progression-free survival (PFS) when using blood (72.2 versus 42.7 months; hazard ratio 0.40, p = 0.0003), but not when using bone marrow. Upon further stratification, positive blood MRD at any level, compared to undetectable blood MRD, was associated with shorter PFS irrespective of clinical complete or partial remission, and a lower 5-year PFS rate irrespective of IGHV-mutated or -unmutated status (all p < 0.05). In conclusion, high-sensitivity (0.0007%) MRD assessment in blood yielded additional prognostic information beyond the current standard sensitivity (0.01%). Our approach provides a model for future determination of the optimal MRD investigative strategy for any regimen.

Validation of a modified pre-lysis sample preparation technique for flow cytometric minimal residual disease assessment in multiple myeloma, chronic lymphocytic leukemia, and B-non Hodgkin lymphoma.

BACKGROUND: Minimal residual disease (MRD) assessment of hematopoietic neoplasia below 10-4 requires more leukocytes than is usually attainable by post-lysis preparation. However, not all laboratories are resourced for consensus Euroflow pre-lysis methodology. Our study aim was to validate a modified pre-lysis protocol against our standard post-lysis method for MRD detection of multiple myeloma (MM), chronic lymphocytic leukemia (CLL), and B-non Hodgkin lymphoma (B-NHL), to meet demand for deeper MRD assessment by flow cytometry. METHOD: Clinical samples for MRD assessment of MM, CLL, and B-NHL (50, 30, and 30 cases, respectively) were prepared in parallel by pre and post-lysis methods for the initial validation. Total leukocytes, MRD, and median fluorescence intensity of antigen expression were compared as measures of sensitivity and antigen stability. Lymphocyte and granulocyte composition were compared, assessing relative sample processing stability. Sensitivity of the pre-lysis assay was monitored post validation for a further 18 months. RESULTS: Pre-lysis achieved at least 10-4 sensitivity in 85% MM, 81% CLL, and 90% B-NHL samples versus 24%, 48%, and 26% by post-lysis, respectively, with stable antigen expression and leukocyte composition. Post validation over 18 months with technical expertise improving, pre-lysis permitted 10-5 MRD assessment in 69%, 86%, and 82% of the respective patient groups. CONCLUSION: This modified pre-lysis procedure provides a sensitive, robust, time efficient, and relatively cost-effective alternative for MRD testing by MFC at 10-5 , facilitating clinically meaningful deeper response assessment for MM, CLL, and B-NHL. This method adaptation may facilitate more widespread adoption of highly sensitive flow cytometry-based MRD assessment.

CD200 Expression in Diagnostic and Prognostic Assessment of Mature B Cell Lymphophoproliferative Neoplasms

Background: Multiparameter flow cytometry is a useful tool for diagnostic evaluation of mature B-cell neoplasms (MBN). Recently, it has been shown that assessment of CD200 expression may improve the distinction between chronic lymphocytic leukemia (CLL; CD200 positive) and mantle cell lymphoma (MCL; CD200 negative), but any potential as a prognostic marker for CLL remains to be established. Materials and methods: This cross sectional study was conducted on sixty-seven patients newly diagnosed as having mature B-cell lymphoproliferative disorders Levels of CD 200 in lymphoma cells were assessed. Results: CD200 was consistently expressed in CLL and hairy cell leukemia B cells, but not in MCL cells. Heterogeneous expression was noted in other CD5 positive Non-Hodgkin lymphomas. High CD200 expression (≥50%) was associated with a higher CD5, 19 and CD23 expression, older age, higher TLC and absolute lymphocyte count, hepatomegaly, splenomegaly and a higher Rai stage. There were no significant correlations between CD200 expression and response to treatment. Conclusion: CD200 could be of high value in distinguishing CLL, MCL, and atypical CLL. CD200 expression can also be of prognostic and therapeutic value in CLL cases.

Drivers of treatment patterns in patients with chronic lymphocytic leukemia stopping ibrutinib or idelalisib therapies.

Novel therapies including kinase inhibitors (KI) have led to high and durable response in patients with chronic lymphocytic leukemia (CLL), however, some patients stop therapy. This study evaluates reasons for treatment changes among CLL patients who stopped KI in real-world practice. Sixty-nine US oncologists/hematologists provided patient-level data abstracted from charts of CLL adult patients who initiated a KI and later (1) switched to another anti-neoplastic regimen (Switched cohort), (2) discontinued the KI and remained untreated (Discontinued cohort), or (3) restarted the same KI after an interruption of ≥60 days (Restarted cohort). Demographics, clinical/treatment characteristics, and reasons for stopping, restarting, and switching the KI therapy were described. In the Switched cohort, reasons for stopping included disease progression (72.5%), low/no disease activity (3.9%), adverse event [AE]/ intolerance/comorbidity (15.7%), and planned cellular therapies (7.9%). In the Discontinued cohort, approximately half (46.0%) of patients stopped KI therapy because they were terminally ill/died, or were moved to best supportive care - these patients were older, had more severe disease, and high comorbidity burden. The other half (54.0% of patients) stopped due to low/no disease activity (24.0%), AEs/toxicity (12.0%), or patient-requested drug holiday (18.0%). In the Restarted cohort, the most common reasons for stopping KIs were patient request (37.3%), AEs/intolerance (31.4%), and economic reasons (10%). Patients restarted when disease progressed (60.8%) or when they recovered from the AE (33%). Reasons for KI stop and subsequent treatment patterns were varied and multifactorial, suggesting heterogeneous disease management and a need for more evidence around supporting strategies and physician education.

iwCLL guidelines for diagnosis, indications for treatment, response assessment, and supportive management of CLL.

The previous edition of the consensus guidelines of the International Workshop on Chronic Lymphocytic Leukemia (iwCLL), published in 2008, has found broad acceptance by physicians and investigators caring for patients with CLL. Recent advances including the discovery of the genomic landscape of the disease, the development of genetic tests with prognostic relevance, and the detection of minimal residual disease (MRD), coupled with the increased availability of novel targeted agents with impressive efficacy, prompted an international panel to provide updated evidence- and expert opinion-based recommendations. These recommendations include a revised version of the iwCLL response criteria, an update on the use of MRD status for clinical evaluation, and recommendations regarding the assessment and prophylaxis of viral diseases during management of CLL.

Assessment of the efficacy of ofatumumab in patients with chronic lymphocytic leukaemia treated in the Department of Haematooncology and Bone Marrow Transplantation of the Medical University in Lublin - Prelimary results.

INTRODUCTION: Despite significant recent advances in the treatment of chronic lymphocytic leukaemia (CLL), most cases of the disease are still incurable. Treatment with monoclonal antibodies, such as ofatumumab, is one of the new therapeutic options. OBJECTIVE: Retrospective analysis of the efficacy of ofatumumab in patients with chronic lymphocytic leukaemia (CLL) treated in the Haematooncology and Bone Marrow Transplantation Department of the Medical University of Lublin, Poland, during 2011-2013. MATERIAL AND METHODS: The analysis included 5 patients (3 women and 2 men), aged 47-65, with Rai stage II-IV CLL, after a few lines of treatment. Three patients received ofatumumab in monotherapy and 2 patients received ofatumumab in combination with cyclophosphamide (50 mg/day) and dexamethasone (40 mg/day). All patients included in the study were diagnosed with an active form of leukaemia with symptoms such as lymphocytosis or massive lymphadenopathy. RESULTS: All patients responded to the treatment. Within the first 8 weeks of the treatment, levels of white blood cells returned to normal in patients with baseline lymphocytosis (3 patients). An increase in platelet levels was reported in 3 patients. Haemoglobin levels were higher or comparable to the baseline values in all studied patients after the completion of immunotherapy. In the patient with massive lymphadenopathy and hepato- and splenomegaly, the size of the lymph nodes, spleen and liver decreased and neutrophil levels increased. Time of progression was 5-12 months, and in one patient partial remission has been maintained. The treatment was well-tolerated in most cases. Asymptomatic neutropenia and an infection with Candida glabrata were observed. CONCLUSIONS: Ofatumumab may be a new and safe therapeutic option for patients with CLL after a few lines of treatment.

Time to Second-line Treatment and Subsequent Relative Survival in Older Patients With Relapsed Chronic Lymphocytic Leukemia/Small Lymphocytic Lymphoma.

BACKGROUND: Novel targeted therapies offer excellent short-term outcomes in patients with chronic lymphocytic leukemia and small lymphocytic lymphoma (CLL/SLL). However, there is disagreement over how widely these therapies should be used in place of standard chemo-immunotherapy (CIT). We investigated whether stratification on the length of the interval between first-line (T1) and second-line (T2) treatments could identify a subgroup of older patients with relapsed CLL/SLL with an expectation of normal overall survival, and for whom CIT could be an acceptable treatment choice. PATIENTS AND METHODS: Patients with relapsed CLL/SLL who received T2 were identified from the SEER-Medicare Linked Database. Five-year relative survival (RS5; ie, the ratio of observed survival to expected survival based on population life tables) was assessed after stratifying patients on the interval between T1 and T2. We then validated our findings in the Mayo Clinic CLL Database. RESULTS: Among 1974 SEER-Medicare patients (median age = 77 years) who received T2 for relapsed CLL/SLL, longer time-to-retreatment was associated with a modestly improved prognosis (P = .01). However, even among those retreated ≥ 3 years after T1, survival was poor compared with the general population (RS5 = 0.50 or lower in SEER-Medicare). Similar patterns were observed in the younger Mayo validation cohort, although prognosis was better overall among the Mayo patients, and patients with favorable fluorescence in situ hybridization retreated ≥ 3 years after T1 had close to normal expected survival (RS5 = 0.87). CONCLUSION: Further research is needed to quantify the degree to which targeted therapies provide meaningful improvements over CIT in long-term outcomes for older patients with relapsed CLL/SLL.

TP53 gene mutation analysis in chronic lymphocytic leukemia by nanopore MinION sequencing.

BACKGROUND: The assessment of TP53 mutational status is becoming a routine clinical practice for chronic lymphocytic leukemia patients (CLL). A broad spectrum of molecular techniques has been employed so far, including both direct Sanger sequencing and next generation sequencing. Oxford Nanopore Technologies recently released the MinION an USB-interfaced sequencer. In this paper we report our experience, with the MinION technology for the detection of the TP53 gene mutation in CLL patients. Twelve CLL patients at diagnosis were included in this study. All except one patient showed the TP53 gene deletion in Fluorescence in situ hybridization experiments. Patients were investigated for TP53 mutation by Sanger and by MinION sequencing. Analysis by Sanger was performed according with the IARC protocol. Analysis by MinION was performed adopting a strategy based on long template PCR, read error correction, and post variant calling filtering. RESULTS: Due to the high error rate of nanopore technology, sequence data were both used directly and before correction with two different in silico methods: ALEC and nanocorrect. A mean error rate of 15 % was detected before correction that was reduced to 4-5 % after correction. Analysis by Sanger sequencing was able to detect four patients mutated for TP53. MinION analysis detected one more mutated patient previously not detected from Sanger. CONCLUSION: In our hands, the Nanopore technology shows correlation with Sanger sequencing but more sensitive, manageable and less expensive, and therefore has proven to be a useful tool for TP53 gene mutation detection.

Minimal Residual Disease Assessment Improves Prediction of Outcome in Patients With Chronic Lymphocytic Leukemia (CLL) Who Achieve Partial Response: Comprehensive Analysis of Two Phase III Studies of the German CLL Study Group.

Purpose To determine the value of minimal residual disease (MRD) assessments, together with the evaluation of clinical response in chronic lymphocytic leukemia according to the 2008 International Workshop on Chronic Lymphocytic Leukemia criteria. Patients and Methods Progression-free survival (PFS) and overall survival of 554 patients from two randomized trials of the German CLL Study Group (CLL8: fludarabine and cyclophosphamide [FC] v FC plus rituximab; CLL10: FC plus rituximab v bendamustine plus rituximab) were analyzed according to MRD assessed in peripheral blood at a threshold of 10-4 and clinical response. The prognostic value of different parameters defining a partial response (PR) was further investigated. Results Patients with MRD-negative complete remission (CR), MRD-negative PR, MRD-positive CR, and MRD-positive PR experienced a median PFS from a landmark at end of treatment of 61 months, 54 months, 35 months, and 21 months, respectively. PFS did not differ significantly between MRD-negative CR and MRD-negative PR; however, PFS was longer for MRD-negative PR than for MRD-positive CR ( P = .048) and for MRD-positive CR compared with MRD-positive PR ( P = .002). Compared with MRD-negative CR, only patients with MRD-positive PR had a significantly shorter overall survival (not reached v 72 months; P = .001), whereas there was no detectable difference for patients with MRD-negative PR or MRD-positive CR ( P = 0.612 and P = 0.853, respectively). Patients with MRD-negative PR who presented with residual splenomegaly had only a similar PFS (63 months) compared with patients with MRD-negative CR (61 months; P = .354), whereas patients with MRD-negative PR with lymphadenopathy showed a shorter PFS (31 months; P < .001). Conclusion MRD quantification allows for improved PFS prediction in both patients who achive PR and CR, which thus supports its application in all responders. In contrast to residual lymphadenopathy, persisting splenomegaly does not impact outcome in patients with MRD-negative PR.

Cost-effectiveness of rituximab in addition to fludarabine and cyclophosphamide (R-FC) for the first-line treatment of chronic lymphocytic leukemia.

The cost-effectiveness of rituximab in combination with fludarabine/cyclophosphamide (R-FC) for the first line treatment of chronic lymphocytic leukemia (CLL) was evaluated. Based on long-term clinical data (follow-up of 5.9 years) from the CLL8-trial, a Markov-model with three health states (Free from disease progression, Progressive disease, Death) was used to evaluate the cost per quality-adjusted life-year (QALY) and cost per life years gained (LYG) of R-FC from the perspective of the German statutory health insurance (SHI). The addition of rituximab to FC chemotherapy results in a gain of 1.1 quality-adjusted life-years. The incremental cost-effectiveness ratio (ICER) of R-FC compared with FC was €17,979 per QALY (€15,773 per LYG). Results were robust in deterministic and probabilistic sensitivity analyses. From the German SHI perspective, rituximab in combination with FC chemotherapy represents good value for first-line treatment of patients with CLL and compares favorably with chemotherapy alone.

Evaluation of geriatric assessment in patients with chronic lymphocytic leukemia: Results of the CLL9 trial of the German CLL study group.

Multidimensional geriatric assessment (GA) has been demonstrated to predict outcomes in older patients with cancer. This study evaluated GA in a cohort of older patients with chronic lymphocytic leukemia (CLL). Seventy-five of 97 subjects with CLL who were enrolled in a clinical trial of the German CLL Study Group underwent GA prior to the start of study treatment (low-dose chemotherapy with fludarabine). GA included cumulative illness rating scale (CIRS), timed-up-and-go (TUG) test, dementia detection (DEMTECT) test and instrumental activities of daily living (IADL) index. There was little correlation between CIRS, TUG, DEMTECT or IADL results and treatment toxicity, feasibility or efficacy in this study. CIRS and IADL had no statistically significant impact on overall prognosis. However, under-performance in TUG or DEMTECT test was strongly associated with poor survival. The latter findings provide a rationale to further investigate geriatric assessment in CLL and in the context with other CLL treatments.

Leukemia in Iran: Epidemiology and Morphology Trends.

BACKGROUND: Leukemia accounts for 8% of total cancer cases and involves all age groups with different prevalence and incidence rates in Iran and the entire world and causes a significant death toll and heavy expenses for diagnosis and treatment processes. This study was done to evaluate epidemiology and morphology of blood cancer during 2003-2008. MATERIALS AND METHODS: This cross- sectional study was carried out based on re- analysis of the Cancer Registry Center report of the Health Deputy in Iran during a 6-year period (2003 - 2008). Statistical analysis for incidence time trends and morphology change percentage was performed with joinpoint regression analysis using the software Joinpoint Regression Program. RESULTS: During the studied years a total of 18,353 hematopoietic and reticuloendothelial system cancers were recorded. Chi square test showed significant difference between sex and morphological types of blood cancer (P-value<0.001). Joinpoint analysis showed a significant increasing trend for the adjusted standard incidence rate (ASIR) for both sexes (P-value<0.05). Annual percent changes (APC) for women and men were 18.7 and 19.9, respectively. The most common morphological blood cancers were ALL, ALM, MM and CLL which accounted for 60% of total hematopoietic system cancers. Joinpoint analyze showed a significant decreasing trend for ALM in both sexes (P-value<0.05). CONCLUSIONS: Hematopoietic system cancers in Iran demonstrate an increasing trend for incidence rate and decreasing trend for ALL, ALM and CLL morphology.

Assessment of p53 and ATM functionality in chronic lymphocytic leukemia by multiplex ligation-dependent probe amplification.

The ATM-p53 DNA-damage response (DDR) pathway has a crucial role in chemoresistance in CLL, as indicated by the adverse prognostic impact of genetic aberrations of TP53 and ATM. Identifying and distinguishing TP53 and ATM functional defects has become relevant as epigenetic and posttranscriptional dysregulation of the ATM/p53 axis is increasingly being recognized as the underlying cause of chemoresistance. Also, specific treatments sensitizing TP53- or ATM-deficient CLL cells are emerging. We therefore developed a new ATM-p53 functional assay with the aim to (i) identify and (ii) distinguish abnormalities of TP53 versus ATM and (iii) enable the identification of additional defects in the ATM-p53 pathway. Reversed transcriptase multiplex ligation-dependent probe amplification (RT-MLPA) was used to measure ATM and/or p53-dependent genes at the RNA level following DNA damage using irradiation. Here, we showed that this assay is able to identify and distinguish three subgroups of CLL tumors (i.e., TP53-defective, ATM-defective and WT) and is also able to detect additional samples with a defective DDR, without molecular aberrations in TP53 and/or ATM. These findings make the ATM-p53 RT-MLPA functional assay a promising prognostic tool for predicting treatment responses in CLL.