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Recent advances in cancer characterization have consistently revealed marked heterogeneity, impeding the completion of integrated molecular and clinical maps for each malignancy. Here, we focus on chronic lymphocytic leukemia (CLL), a B cell neoplasm with variable natural history that is conventionally categorized into two subtypes distinguished by extent of somatic mutations in the heavy-chain variable region of immunoglobulin genes (IGHV). To build the ‘CLL map,’ we integrated genomic, transcriptomic and epigenomic data from 1,148 patients. We identified 202 candidate genetic drivers of CLL (109 new) and refined the characterization of IGHV subtypes, which revealed distinct genomic landscapes and leukemogenic trajectories. Discovery of new gene expression subtypes further subcategorized this neoplasm and proved to be independent prognostic factors. Clinical outcomes were associated with a combination of genetic, epigenetic and gene expression features, further advancing our prognostic paradigm. Overall, this work reveals fresh insights into CLL oncogenesis and prognostication. A genomic, transcriptomic and epigenomic analysis of chronic lymphocytic leukemia identifies genetic drivers and molecular subtypes associated with clinical outcomes.

Defects in apoptosis can promote tumorigenesis and impair responses of malignant B cells to chemotherapeutics. Members of the B-cell leukemia/lymphoma-2 (BCL-2) family of proteins are key regulators of the intrinsic, mitochondrial apoptotic pathway. Overexpression of antiapoptotic BCL-2 family proteins is associated with treatment resistance and poor prognosis. Thus, inhibition of BCL-2 family proteins is a rational therapeutic option for malignancies that are dependent on antiapoptotic BCL-2 family proteins. Venetoclax (ABT-199, GDC-0199) is a highly selective BCL-2 inhibitor that represents the first approved agent of this class and is currently widely used in the treatment of chronic lymphocytic leukemia (CLL) as well as acute myeloid leukemia (AML). Despite impressive clinical activity, venetoclax monotherapy for a prolonged duration can lead to drug resistance or loss of dependence on the targeted protein. In this review, we provide an overview of the mechanism of action of BCL-2 inhibition and the role of this approach in the current treatment paradigm of B-cell malignancies. We summarize the drivers of de novo and acquired resistance to venetoclax that are closely associated with complex clonal shifts, interplay of expression and interactions of BCL-2 family members, transcriptional regulators, and metabolic modulators. We also examine how tumors initially resistant to venetoclax become responsive to it following prior therapies. Here, we summarize preclinical data providing a rationale for efficacious combination strategies of venetoclax to overcome therapeutic resistance by a targeted approach directed against alternative antiapoptotic BCL-2 family proteins (MCL-1, BCL-xL), compensatory prosurvival pathways, epigenetic modifiers, and dysregulated cellular metabolism/energetics for durable clinical remissions.

Richter transformation (RT) is a paradigmatic evolution of chronic lymphocytic leukemia (CLL) into a very aggressive large B cell lymphoma conferring a dismal prognosis. The mechanisms driving RT remain largely unknown. We characterized the whole genome, epigenome and transcriptome, combined with single-cell DNA/RNA-sequencing analyses and functional experiments, of 19 cases of CLL developing RT. Studying 54 longitudinal samples covering up to 19 years of disease course, we uncovered minute subclones carrying genomic, immunogenetic and transcriptomic features of RT cells already at CLL diagnosis, which were dormant for up to 19 years before transformation. We also identified new driver alterations, discovered a new mutational signature (SBS-RT), recognized an oxidative phosphorylation (OXPHOS) high –B cell receptor (BCR) low -signaling transcriptional axis in RT and showed that OXPHOS inhibition reduces the proliferation of RT cells. These findings demonstrate the early seeding of subclones driving advanced stages of cancer evolution and uncover potential therapeutic targets for RT. Single-cell genomic and transcriptomic analyses of longitudinal samples of patients with Richter syndrome reveal the presence and dynamics of clones driving transformation from chronic lymphocytic leukemia years before clinical manifestation

In chronic lymphocytic leukemia (CLL), TP53 gene defects, due to deletion of the 17p13 locus and/or mutation(s) within the TP53 gene, are associated with resistance to chemoimmunotherapy and a particularly dismal clinical outcome. On these grounds, analysis of TP53 aberrations has been incorporated into routine clinical diagnostics to improve patient stratification and optimize therapeutic decisions. The predictive implications of TP53 aberrations have increasing significance in the era of novel targeted therapies, i.e., inhibitors of B-cell receptor (BcR) signaling and anti-apoptotic BCL2 family members, owing to their efficacy in patients with TP53 defects. In this report, the TP53 Network of the European Research Initiative on Chronic Lymphocytic Leukemia (ERIC) presents updated recommendations on the methodological approaches for TP53 mutation analysis. Moreover, it provides guidance to ensure that the analysis is performed in a timely manner for all patients requiring treatment and that the data is interpreted and reported in a consistent, standardized, and accurate way. Since next-generation sequencing technologies are gaining prominence within diagnostic laboratories, this report also offers advice and recommendations for the interpretation of TP53 mutation data generated by this methodology.

Key Points Chronic lymphocytic leukaemia (CLL), the most common leukaemia in the Western world, is a heterogeneous disease, comprising two main subtypes (known as immunoglobulin heavy chain variable region-mutated ( IGHV -M) and IGHV -unmutated ( IGHV -UM) CLLs). These subtypes are historically associated with a good and a poor prognosis, respectively, and differ in underlying genetic lesions, degree of genetic clonal evolution, epigenetic changes, activated signalling pathways and microenvironmental interactions. CLL is preceded by an asymptomatic precursor termed monoclonal B cell lymphocytosis (MBL). Traditionally, the two most aggressive clinical types of CLL are those resistant to fludarabine or those transforming to aggressive lymphomas of the diffuse large B cell lymphoma (DLBCL) type, known as Richter syndrome. Although CLL may originate at the haematopoietic stem cell (HSC) stage, the final mature B cell of origin of IGHV -M CLL seems to be a post-GC CD5 + CD27 + B cell, and that of IGHV -UM CLL could be a pre-GC CD5 + CD27 − B cell or a GC-independent memory B cell. B cell receptor (BCR) signalling has an important role in the pathogenesis of CLL, as demonstrated by the presence of a highly restricted and biased repertoire of surface immunoglobulin (sIg) in CLL cells, evidence of autonomous BCR signalling and dramatic clinical responses obtained with BCR pathway inhibitors. The CLL genome displays a relatively low mutational burden and is characterized by a small number of frequently mutated putative 'driver' genes and a large number of rarely altered genes. The CLL epigenome is characterized by widespread hypomethylation of DNA in genes and enhancer loci. A subset of genes mutated in CLL confer a poor outcome in patients with CLL and can improve the classic cytogenetics-based prognostic classification of patients with CLL. Also subclonal high-risk genetic lesions can have a negative impact on the outcome of patients with CLL. Intra-sample genetic and epigenetic heterogeneity are both associated with overall poor survival of patients with CLL. This Review discusses the molecular biology underlying chronic lymphocytic leukaemia (CLL). Emphasizing the role of genetic lesions in CLL initiation and clinical progression, the article also considers the clinical implications of these findings. Recent investigations have provided an increasingly complete picture of the genetic landscape of chronic lymphocytic leukaemia (CLL). These analyses revealed that the CLL genome displays a high degree of heterogeneity between patients and within the same patient. In addition, they highlighted molecular mechanisms and functionally relevant biological programmes that may be important for the pathogenesis and therapeutic targeting of this disease. This Review focuses on recent insights into the understanding of CLL biology, with emphasis on the role of genetic lesions in the initiation and clinical progression of CLL. We also consider the translation of these findings into the development of risk-adapted and targeted therapeutic approaches.

Richter syndrome (RS) arising from chronic lymphocytic leukemia (CLL) exemplifies an aggressive malignancy that develops from an indolent neoplasm. To decipher the genetics underlying this transformation, we computationally deconvoluted admixtures of CLL and RS cells from 52 patients with RS, evaluating paired CLL–RS whole-exome sequencing data. We discovered RS-specific somatic driver mutations (including IRF2BP2 , SRSF1 , B2M , DNMT3A and CCND3 ), recurrent copy-number alterations beyond del(9p21)( CDKN2A/B ), whole-genome duplication and chromothripsis, which were confirmed in 45 independent RS cases and in an external set of RS whole genomes. Through unsupervised clustering, clonally related RS was largely distinct from diffuse large B cell lymphoma. We distinguished pathways that were dysregulated in RS versus CLL, and detected clonal evolution of transformation at single-cell resolution, identifying intermediate cell states. Our study defines distinct molecular subtypes of RS and highlights cell-free DNA analysis as a potential tool for early diagnosis and monitoring. Integrative genomic and transcriptomic analyses reveal molecular events defining Richter transformation from CLL, and highlight the potential of cell-free DNA for early detection.

Cancers are caused by genomic alterations known as drivers. Hundreds of drivers in coding genes are known but, to date, only a handful of noncoding drivers have been discovered—despite intensive searching 1 , 2 . Attention has recently shifted to the role of altered RNA splicing in cancer; driver mutations that lead to transcriptome-wide aberrant splicing have been identified in multiple types of cancer, although these mutations have only been found in protein-coding splicing factors such as splicing factor 3b subunit 1 ( SF3B1 ) 3 – 6 . By contrast, cancer-related alterations in the noncoding component of the spliceosome—a series of small nuclear RNAs (snRNAs)—have barely been studied, owing to the combined challenges of characterizing noncoding cancer drivers and the repetitive nature of snRNA genes 1 , 7 , 8 . Here we report a highly recurrent A>C somatic mutation at the third base of U1 snRNA in several types of tumour. The primary function of U1 snRNA is to recognize the 5′ splice site via base-pairing. This mutation changes the preferential A–U base-pairing between U1 snRNA and the 5′ splice site to C–G base-pairing, and thus creates novel splice junctions and alters the splicing pattern of multiple genes—including known drivers of cancer. Clinically, the A>C mutation is associated with heavy alcohol use in patients with hepatocellular carcinoma, and with the aggressive subtype of chronic lymphocytic leukaemia with unmutated immunoglobulin heavy-chain variable regions. The mutation in U1 snRNA also independently confers an adverse prognosis to patients with chronic lymphocytic leukaemia. Our study demonstrates a noncoding driver in spliceosomal RNAs, reveals a mechanism of aberrant splicing in cancer and may represent a new target for treatment. Our findings also suggest that driver discovery should be extended to a wider range of genomic regions. A highly recurrent A>C somatic mutation in U1 small nuclear RNA, which alters the splicing pattern of genes that include known drivers of cancer, is identified in several types of tumour.

Data on long-term outcomes and biological drivers associated with depth of remission after BCL2 inhibition by venetoclax in the treatment of chronic lymphocytic leukemia (CLL) are limited. In this open-label parallel-group phase-3 study, 432 patients with previously untreated CLL were randomized (1:1) to receive either 1-year venetoclax-obinutuzumab (Ven-Obi, 216 patients) or chlorambucil-Obi (Clb-Obi, 216 patients) therapy (NCT02242942). The primary endpoint was investigator-assessed progression-free survival (PFS); secondary endpoints included minimal residual disease (MRD) and overall survival. RNA sequencing of CD19-enriched blood was conducted for exploratory post-hoc analyses. After a median follow-up of 65.4 months, PFS is significantly superior for Ven-Obi compared to Clb-Obi (Hazard ratio [HR] 0.35 [95% CI 0.26–0.46], p  < 0.0001). At 5 years after randomization, the estimated PFS rate is 62.6% after Ven-Obi and 27.0% after Clb-Obi. In both arms, MRD status at the end of therapy is associated with longer PFS. MRD + ( ≥ 10 −4 ) status is associated with increased expression of multi-drug resistance gene ABCB1 (MDR1) , whereas MRD6 (< 10 −6 ) is associated with BCL2L11 ( BIM ) expression. Inflammatory response pathways are enriched in MRD+ patient solely in the Ven-Obi arm. These data indicate sustained long-term efficacy of fixed-duration Ven-Obi in patients with previously untreated CLL. The distinct transcriptomic profile of MRD+ status suggests possible biological vulnerabilities. The CLL14 study (NCT02242942) explored the activity of obinutuzumab (anti-CD20) plus venetoclax (Bcl2 inhibitor) versus obinutuzumab plus chlorambucil in patients with previously untreated chronic lymphocytic leukemia (CLL). Here the authors report the 5-year long-term results of the clinical trial and transcriptional profiles associated with response to therapies.

B cell receptor (BCR) signalling is crucial for normal B cell development and adaptive immunity. BCR signalling also supports the survival and growth of malignant B cells in patients with B cell leukaemias or lymphomas. The mechanism of BCR pathway activation in these diseases includes continuous BCR stimulation by microbial antigens or autoantigens present in the tissue microenvironment, activating mutations within the BCR complex or downstream signalling components and ligand-independent tonic BCR signalling. The most established agents targeting BCR signalling are Bruton tyrosine kinase (BTK) inhibitors and PI3K isoform-specific inhibitors, and their introduction into the clinic is rapidly changing how B cell malignancies are treated. B cells and BCR-related kinases, such as BTK, also play a role in the microenvironment of solid tumours, such as squamous cell carcinoma and pancreatic cancer, and therefore targeting B cells or BCR-related kinases may have anticancer activity beyond B cell malignancies.

Assessment of measurable residual disease (often referred to as “minimal residual disease”) has emerged as a highly sensitive indicator of disease burden during and at the end of treatment and has been correlated with time-to-event outcomes in chronic lymphocytic leukemia. Undetectable-measurable residual disease status at the end of treatment demonstrated independent prognostic significance in chronic lymphocytic leukemia, correlating with favorable progression-free and overall survival with chemoimmunotherapy. Given its utility in evaluating depth of response, determining measurable residual disease status is now a focus of outcomes in chronic lymphocytic leukemia clinical trials. Increased adoption of measurable residual disease assessment calls for standards for nomenclature and outcomes data reporting. In addition, many basic questions have not been systematically addressed. Here, we present the work of an international, multidisciplinary, 174-member panel convened to identify critical questions on key issues pertaining to measurable residual disease in chronic lymphocytic leukemia, review evaluable data, develop unified answers in conjunction with local expert input, and provide recommendations for future studies. Recommendations are presented regarding methodology for measurable residual disease determination, assay requirements and in which tissue to assess measurable residual disease, timing and frequency of assessment, use of measurable residual disease in clinical practice versus clinical trials, and the future usefulness of measurable residual disease assessment. Nomenclature is also proposed. Adoption of these recommendations will work toward standardizing data acquisition and interpretation in future studies with new treatments with the ultimate objective of improving outcomes and curing chronic lymphocytic leukemia.