Reichard, Kaaren K.

Abstract Background Although myeloproliferative neoplasm-unclassifiable (MPN-U) stands as a distinct entity in the International Consensus Classification (ICC) for myeloproliferative neoplasms, its diagnosis and management remain challenging due to the overlapping clinico-pathological characteristics with other MPNs. In the current study, we describe a well-defined cohort of patients with MPN-U and compare their presentation and outcome with those of a separate cohort with essential thrombocythemia (ET). Methods Diagnostic criteria were according to the ICC (Blood 2022; 140:1200). Non-driver mutations were screened by next-generation sequencing (NGS) and were available for subsets of patients with MPN-U or ET. Conventional statistical methods were employed, using JMP Pro 18.0.0 software SAS Institute, Cary, NC, USA. Results Thirty Mayo Clinic patients who met the ICC criteria for MPN-U (median age 64 years; range 33-94; 60% males) and 658 with ET (median age 60 years; range 18-90; 36% males) were included in the current study. Table 1 outlines a comparative list of presenting characteristics (including mutations), clinical outcomes, and treatment details between patients with MPN-U vs. ET. JAK2 mutations were significantly more prevalent in MPN-U cohort (87% vs. 63% in ET; p<0.01) and CALR mutations less common (3% vs. 25%; p<0.01). Other somatic mutations, including ASXL1, SRSF2, and EZH2 were more frequently observed in the MPN-U group (p<0.05 in all). Abnormal karyotype was reported in 14% of patients with MPN-U vs. 8% with ET (p=0.3). Compared to patients with ET, those with MPN-U were more likely to be males (60% vs. 36%; p<0.01) and, as expected from disease presentation and indications for diagnostic work up of suspected cases, present with venous thrombosis (43% vs. 10%; p<0.01) and palpable splenomegaly (40% vs. 8.5%; p<0.01). Similarly, they were less likely to display thrombocytosis or leukocytosis (p<0.01 for both). Portal, superior mesenteric, and hepatic vein thromboses constituted 77% (vs. 27% in ET; p<0.01) of the venous events in MPN-U; in contrast, the incidences of pre-diagnosis arterial events were similar between the two groups (10% vs. 12%; p=0.7). At a median follow-up of 2.8 years in the MPN-U cohort, 6 (20%) deaths and 1 (3%) leukemic transformation were documented while 3 (10%) patients progressed to meet the diagnostic criteria for polycythemia vera. Four (13%) patients with MPN-U experienced venous thrombo-embolic events (VTEs) including 2 with recurrent VTEs, despite active therapy with systemic anticoagulation and aspirin. The ET cohort was followed for a median of 7.3 years with 161 (24%) deaths, 23 (3%) leukemic transformations, and 66 (10%) VTEs. Among the latter, 27 (41%) had recurrent episodes despite treatment with systemic anticoagulation, aspirin, and/or cytoreductive drugs. Notably, patients with MPN-U were less likely to receive aspirin and cytoreductive therapy during the clinical course (77% vs. 91% and 37% vs. 79%; p<0.01 for both, respectively). Long-term survival rates were similar between MPN-U and ET (15-year survival 70% vs. 65%; p=0.1). Consistent with previous associations seen in ET, patients with JAK2-mutated MPN-U were more likely to be males (58% vs. 30%; p<0.01, Table 2), and display a lower platelet and leukocyte count at the time of diagnosis (p<0.01 for both). These patients were also more likely to present with venous thrombosis (50% vs. 12% in JAK2 wild-type cases; p<0.01) and palpable splenomegaly (46% vs. 9%; p<0.01). Of note, the incidences of pre- and post-diagnosis arterial and post-diagnosis venous events were similar between JAK2-mutated MPN-U vs. JAK2-mutated ET patients (12% vs. 14%; p=0.7, 4% vs. 12.5%; p=0.1, and 15% vs. 12%, p=0.6, respectively). Similarly, long-term outcomes including deaths (15% vs. 26%; p=0.2), leukemic transformations (4% vs. 4%; p=0.9), and 15-year survival rates (78% vs. 60%; p=0.9) were also comparable between the two groups. Conclusion The findings from the current study were not unexpected and underline the ongoing challenges that face formal classification systems in formulating accurate diagnostic criteria for patients with MPN-U whose clinical presentation is biased by disease definitions. Regardless, it is comforting to document a favorable long-term outcome that appeared to be similar to that of ET while venous thrombosis remains a treatment challenge in both groups.

ABSTRACT Background Chronic myelomonocytic leukemia (CMML) is largely a disease of individuals older than 50 years; its occurrence in patients aged 50 years and younger is rare. The authors sought to characterize the clinicopathologic features and genetic profile of young‐onset (age 50 years and younger) CMML (y‐CMML) compared with older onset (older than 50 years) CMML (o‐CMML). Methods The authors conducted a multi‐institutional study of 32 patients with y‐CMML and 119 patients with o‐CMML, analyzing clinical, morphologic, cytogenetic, and molecular data. Results Patients who had y‐CMML frequently presented with splenomegaly (59% vs. 11%; p < .001) and hepatomegaly (25% vs. 2%; p < .001) compared with those who had o‐CMML. Although the overall incidence of cytogenetic abnormalities was similar, patients who had y‐CMML exhibited distinct mutational patterns. PTPN11 mutations were significantly more common in y‐CMML (13% vs. 3%; p = .034) than in o‐CMML, whereas TET2 (6% vs. 57%; p < .001) and SRSF2 (16% vs. 46%; p = .002) mutations were significantly less frequent. In addition, multi‐hit TET2 (6% vs. 34%; p = .002) and TET2‐SRSF2 (3% vs. 29%; p = .003) co‐mutations were rare in y‐CMML. However, the molecular differences did not affect the CMML‐specific risk‐stratification categories because the clinical outcomes, including overall survival and leukemia‐free survival, did not differ between the two groups. Conclusions CMML in patients aged 50 years and younger is rare and presents with unique clinical and mutational features, suggesting a distinct pathogenesis.

ABSTRACT The World Health Organization (WHO) 5th Edition and International Consensus Classification (ICC) have continued to delineate more genetically defined acute leukemias. Both recognize genetic aberrations associated with myelodysplastic syndromes/neoplasms (MDS) as defining MDS‐related AML (AML‐MR). Mutations in RUNX1 are included in this category in the ICC, but not WHO. The current classifications are unclear on how acute leukemias with ambiguous lineage (ALAL), including those of mixed lineage (MPAL) and those without a defined lineage (AUL), should be categorized in the presence of such mutations. Our multi‐institutional study aims to determine the significance of RUNX1 mutation in ALAL compared to de novo AML. Newly diagnosed MPAL, AUL, and AML with RUNX1 mutations were collected. ALAL with MDS‐related cytogenetics, BCR::ABL1 , KMT2A rearrangements, or ZNF384 or BCL11b abnormalities were excluded. We analyzed 17 cases of ALAL and 71 cases of AML that met inclusion criteria. ALAL‐ RUNX1 and AML‐ RUNX1 showed overlapping mutational landscapes with frequent comutations in MDS‐associated genes. No ALAL‐ RUNX1 or AML‐ RUNX1 cases showed concomitant TP53 mutation. ALAL‐ RUNX1 had more bone marrow blasts and more karyotypic abnormalities; however, neither impacted survival, nor did RUNX1 variant allele frequency (VAF). Survival analysis revealed similarly poor outcomes between them. AML‐directed therapies and allogeneic hematopoietic stem cell transplant trended toward improved survival in ALAL‐ RUNX1; however, it did not reach significance. Our results suggest ALAL‐ RUNX1 is associated with younger age, higher blasts, and more karyotypic abnormalities, but has similar clinical and genetic features and outcomes to AML‐ RUNX1 . Our findings suggest, like other MR mutations, RUNX1 ‐mutated ALALs should be included within AML‐MR.

Abstract Objective Gastrointestinal (GI) symptoms are common in systemic mastocytosis (SM). We hereby report the clinicopathologic and molecular features of GI mastocytosis. Methods The study includes 104 patients with suspected SM. Of 258 GI biopsy ­specimens, 33 (20 patients, 19%) were mastocytosis-positive, with 19 (16 patients) initially missed. Results Tryptase (n = 29) was weakly positive/negative in two-thirds of the mastocytosis-positive GI biopsy specimens. Additional immunohistochemistry (n = 23) showed positive mast cell expression for CD30 (n = 2), CD123 (n = 7), and PD-L1 (n = 12), as well as increased PD-1–positive cells (n = 4). Sixty patients had positive bone marrow (BM) for SM (SM-BM+), including 19 with positive GI biopsy specimens (SM-GI+). Almost all (43/44) SM-BM– patients were SM-GI–. The SM-GI vs SM-BM status showed high positive predictive value (95%) and specificity (98%). Patients with SM with mastocytosis-positive vs mastocytosis-negative GI biopsy specimens had higher serum tryptase levels (P = .04). KIT D816V mutation was detected in 7 of 13 and 12 of 13 mastocytosis-positive GI biopsy specimens using allele-specific polymerase chain reaction and droplet digital polymerase chain reaction (ddPCR), respectively. Conclusions GI mastocytosis is highly predictive of SM in BM; however, most SM-BM+ patients are SM-GI–. The SM-BM– patients are very unlikely to be SM-GI+. Because GI neoplastic mast cells are often tryptase negative, diagnostic evaluation should include CD117 and CD25 immunohistochemistry, as well as KIT D816V mutation analysis by ddPCR as needed.

ABSTRACT Survival prediction models in essential thrombocythemia (ET) include the International Prognostic Scoring System (IPSET) and the more recently introduced triple‐A (AAA) prognostic score. The latter enlists age and absolute neutrophil (ANC) and lymphocyte (ALC) counts as risk variables. In the current study, a Mayo Clinic discovery cohort of 658 patients with ET was used to identify AAA‐independent risk variables. Accordingly, multivariable analysis‐derived HRs (95% CI) were 15.7 (8.4–29.5) for age > 70 years (8 points); 4.2 (2.3–7.5) for age 50 to 70 years (2 points); 1.8 (1.2–2.5) for ANC ≥ 8 × 10 9 /L (1 point); 1.4 (1.03–1.9) for ALC < 1.7 × 10 9 /L (1 point); 1.8 (1.2–2.6) for absolute monocyte count (AMC) ≥ 0.5 × 10 9 /L (1 point); 1.8 (1.2–2.3) for male sex (1 point); 1.8 (1.3–2.4) for arterial hypertension (1 point); and 1.6 (1.2–2.3) for arterial thrombosis (1 point). HR‐weighted scoring enabled a 4‐tiered risk classification: ultra‐low (0–1 points; N = 94; median survival 42.7 years), low (2–4 points; N = 297; 23 years), intermediate (5 points; N = 66; 17.3 years), and high (6–14 points; N = 201; 10.8 years). Time‐dependent predictive performance at 20/25 years favored AAA + (AUC 0.92/0.91) vs. AAA (0.86/0.86) vs. IPSET (0.81/0.84). The AAA + risk model was subsequently validated by two external cohorts from Israel ( N = 5968) and Italy ( N = 682). In the cohort from Israel, disease‐specific mortality was assessed by comparing observed survival to an age‐ and sex‐matched reference population, which suggested near‐normal life expectancy in ultra‐low risk patients. The current study highlights host‐related factors as the primary determinants of longevity in ET and provides a composite risk score (AAA + ) that is based on complete blood count‐derived parameters and host‐related factors. Predictive performance of the new model was shown to be superior to that of IPSET and AAA.

ABSTRACTThe current study includes 910 patients with systemic mastocytosis (SM) seen at the Mayo Clinic from 1968 to 2024. The primary objective was to examine the prognostic contribution of the International Consensus Classification (ICC), in the context of the Mayo Alliance Prognostic System (MAPS) for SM. World Health Organization classification (WHO‐HAEM5) subcategories included (i) indolent/smoldering SM (ISM/SSM; N = 518), (ii) SM associated with another hematological neoplasm (SM‐AHN; N = 273), with the latter including both myeloid and lymphoid neoplasms, (iii) aggressive SM (ASM; N = 106), and (iv) WHO‐defined mast cell leukemia (MCL; N = 13), which included mast cells with both “mature” and “immature” morphology. The ICC‐defined subcategories were mostly similar with the exception that SM‐AHN was replaced by SM associated with another myeloid neoplasm (SM‐AMN; N = 235) and WHO‐defined MCL was replaced by ICC‐defined MCL (N = 8), which included only those with immature MC morphology. Overall survival (OS) was similar between WHO‐defined MCL (median 1.8 years) vs. SM‐AHN (median 2.3 years; p = 0.3) but significantly different between ICC‐defined MCL (median 0.08 years) vs. SM‐AMN (median 2.0 years; p < 0.01). Significant difference in OS was also apparent between ICC‐defined SM‐AMN and SM associated with lymphoid neoplasm (SM‐ALN; median 8.1 years; HR 3.4; p < 0.01). Multivariable analysis confirmed the inter‐independent prognostic contributions of both ICC‐defined morphologic subcategories and MAPS risk variables, including age > 60 years, anemia, alkaline phosphatase > ULN, and platelet count < 150 × 109/L (p < 0.03 in all instances); the same was not true for WHO‐HAEM5‐defined SM subcategories. The addition of mutational information into the multivariable model resulted in ousting anemia and inclusion of ASXL1 (p < 0.01), SRSF2 (p = 0.01), and NRAS (p = 0.01) mutations as additional risk factors. Classification of SM by ICC is prognostically more accurate, compared to WHO‐HAEM5, and strengthens the prognostic contribution of morphology to current clinical and molecular risk models.

Abstract Objective The successful diagnosis and classification of lymphoid neoplasms in blood and bone marrow is the responsibility of the practicing pathologist. This guide provides a general “roadmap” for this process, from initial case recognition to final classification. Methods The integration of hematologic, morphologic, immunophenotypic, and genetic features for the full spectrum of precursor and mature B-cell, T-cell, and natural killer–cell neoplasms that typically manifest in blood and bone marrow is included. Results Classification systems for lymphoid neoplasms provide criteria for pathologists to render a diagnosis that is optimal for patient care, treatment, and outcome prediction. Conclusions This guide provides diagnostic strategies for lymphoid neoplasms encountered in blood and bone marrow specimens using both the International Consensus Classification and the World Health Organization fifth edition classification systems. Key tips are provided for each entity along with testing requirements, differential diagnosis, nonneoplastic mimics, and other unique features based on the experience of the Bone Marrow Pathology Group members.