The upcoming 5th edition of the World Health Organization (WHO) Classification of Haematolymphoid Tumours is part of an effort to hierarchically catalogue human cancers arising in various organ systems within a single relational database. This paper summarizes the new WHO classification scheme for myeloid and histiocytic/dendritic neoplasms and provides an overview of the principles and rationale underpinning changes from the prior edition. The definition and diagnosis of disease types continues to be based on multiple clinicopathologic parameters, but with refinement of diagnostic criteria and emphasis on therapeutically and/or prognostically actionable biomarkers. While a genetic basis for defining diseases is sought where possible, the classification strives to keep practical worldwide applicability in perspective. The result is an enhanced, contemporary, evidence-based classification of myeloid and histiocytic/dendritic neoplasms, rooted in molecular biology and an organizational structure that permits future scalability as new discoveries continue to inexorably inform future editions.

The BCL-2 inhibitor venetoclax combined with hypomethylating agents or low-dose cytarabine represents an important new therapy for older or unfit patients with acute myeloid leukemia (AML). We analyzed 81 patients receiving these venetoclax-based combinations to identify molecular correlates of durable remission, response followed by relapse (adaptive resistance), or refractory disease (primary resistance). High response rates and durable remissions were typically associated with NPM1 or IDH2 mutations, with prolonged molecular remissions prevalent for NPM1 mutations. Primary and adaptive resistance to venetoclax-based combinations was most commonly characterized by acquisition or enrichment of clones activating signaling pathways such as FLT3 or RAS or biallelically perturbing TP53. Single-cell studies highlighted the polyclonal nature of intratumoral resistance mechanisms in some cases. Among cases that were primary refractory, we identified heterogeneous and sometimes divergent interval changes in leukemic clones within a single cycle of therapy, highlighting the dynamic and rapid occurrence of therapeutic selection in AML. In functional studies, FLT3 internal tandem duplication gain or TP53 loss conferred cross-resistance to both venetoclax and cytotoxic-based therapies. Collectively, we highlight molecular determinants of outcome with clinical relevance to patients with AML receiving venetoclax-based combination therapies.

Clonal diversity is a consequence of cancer cell evolution driven by Darwinian selection. Precise characterization of clonal architecture is essential to understand the evolutionary history of tumor development and its association with treatment resistance. Here, using a single-cell DNA sequencing, we report the clonal architecture and mutational histories of 123 acute myeloid leukemia (AML) patients. The single-cell data reveals cell-level mutation co-occurrence and enables reconstruction of mutational histories characterized by linear and branching patterns of clonal evolution, with the latter including convergent evolution. Through xenotransplantion, we show leukemia initiating capabilities of individual subclones evolving in parallel. Also, by simultaneous single-cell DNA and cell surface protein analysis, we illustrate both genetic and phenotypic evolution in AML. Lastly, single-cell analysis of longitudinal samples reveals underlying evolutionary process of therapeutic resistance. Together, these data unravel clonal diversity and evolution patterns of AML, and highlight their clinical relevance in the era of precision medicine.

Myeloid neoplasms and acute leukemias derive from the clonal expansion of hematopoietic cells driven by somatic gene mutations. Although assessment of morphology plays a crucial role in the diagnostic evaluation of patients with these malignancies, genomic characterization has become increasingly important for accurate diagnosis, risk assessment, and therapeutic decision making. Conventional cytogenetics, a comprehensive and unbiased method for assessing chromosomal abnormalities, has been the mainstay of genomic testing over the past several decades and remains relevant today. However, more recent advances in sequencing technology have increased our ability to detect somatic mutations through the use of targeted gene panels, whole-exome sequencing, whole-genome sequencing, and whole-transcriptome sequencing or RNA sequencing. In patients with myeloid neoplasms, whole-genome sequencing represents a potential replacement for both conventional cytogenetic and sequencing approaches, providing rapid and accurate comprehensive genomic profiling. DNA sequencing methods are used not only for detecting somatically acquired gene mutations but also for identifying germline gene mutations associated with inherited predisposition to hematologic neoplasms. The 2022 International Consensus Classification of myeloid neoplasms and acute leukemias makes extensive use of genomic data. The aim of this report is to help physicians and laboratorians implement genomic testing for diagnosis, risk stratification, and clinical decision making and illustrates the potential of genomic profiling for enabling personalized medicine in patients with hematologic neoplasms.

Nucleophosmin-1 mutations (NPM1+) occur in ∼30% of acute myeloid leukemia (AML) patients. Although typically associated with favorable prognosis, the beneficial impact of NPM1+ decreases with increasing age in patients treated with standard intensive chemotherapy (IC) or hypomethylating agents (HMAs). This retrospective analysis compared outcomes of NPM1+ AML patients treated with 1 of 3 induction approaches: HMA plus BCL-2 inhibitor venetoclax (VEN), HMA, or IC therapy. Composite complete response (CRc: CR + CR with incomplete count recovery) was seen in 96% (27/28), 36% (17/47), and 89% (204/228) of HMA + VEN, HMA, and IC patients, respectively (HMA + VEN vs HMA, P < .001; HMA + VEN vs IC, P = .10). Older patients (age >65 years) treated with HMA + VEN, HMA, or IC had CR rates of 88%, 28%, and 56%, respectively (HMA + VEN vs HMA, P < .001; HMA + VEN vs IC, P = .01). Significant improvement in overall survival (OS) was seen in patients age >65 years treated with HMA + VEN vs HMA (not reached [NR] vs 0.4 years; P < .001) or IC (NR vs 0.93 years; P = .001). Older patients treated with HMA + VEN had OS of 80% after median 1-year follow-up, with estimated 2-year OS of 70%. In the multivariable Cox model analysis, HMA + VEN was associated with a 69% lower risk of death compared with IC (hazard ratio, 0.31; 95% confidence interval, 0.12-0.83; type I error–adjusted P = .038). HMA + VEN combinations demonstrated impressive results compared with traditional standard-of-care regimens in older patients with NPM1+ AML.

The safety and efficacy of combining the isocitrate dehydrogenase-1 (IDH1) inhibitor ivosidenib (IVO) with the BCL2 inhibitor venetoclax (VEN; IVO + VEN) ± azacitidine (AZA; IVO + VEN + AZA) were evaluated in four cohorts of patients with IDH1-mutated myeloid malignancies (n = 31). Most (91%) adverse events were grade 1 or 2. The maximal tolerated dose was not reached. Composite complete remission with IVO + VEN + AZA versus IVO + VEN was 90% versus 83%. Among measurable residual disease (MRD)-evaluable patients (N = 16), 63% attained MRD-negative remissions; IDH1 mutation clearance occurred in 64% of patients receiving ≥5 treatment cycles (N = 14). Median event-free survival and overall survival were 36 [94% CI, 23–not reached (NR)] and 42 (95% CI, 42-NR) months. Patients with signaling gene mutations appeared to particularly benefit from the triplet regimen. Longitudinal single-cell proteogenomic analyses linked cooccurring mutations, antiapoptotic protein expression, and cell maturation to therapeutic sensitivity of IDH1-mutated clones. No IDH isoform switching or second-site IDH1 mutations were observed, indicating combination therapy may overcome established resistance pathways to single-agent IVO. Significance: IVO + VEN + AZA is safe and active in patients with IDH1-mutated myeloid malignancies. Combination therapy appears to overcome resistance mechanisms observed with single-agent IDH-inhibitor use, with high MRD-negative remission rates. Single-cell DNA ± protein and time-of-flight mass-cytometry analysis revealed complex resistance mechanisms at relapse, highlighting key pathways for future therapeutic intervention. Watch the interview with Courtney D. DiNardo, MD, MSCE, recipient of the 2025 Blood Cancer Discovery Award for Outstanding Journal Article: https://vimeo.com/1100470320 This article is highlighted in the In This Issue feature, p. 247