Pardanani, Animesh

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.

e18523 Background: Allogeneic hematopoietic stem cell transplant (AHCT) remains the only curative option for genetically high-risk acute myeloid leukemia (AML). Venetoclax plus hypomethylating agents (Ven+HMA) is approved as frontline treatment in elderly patients with AML ( NEJM 2020; 383); however, less is known on the post-transplant outcomes following such therapy. Methods: Newly diagnosed (ND) AML patients who received Ven+HMA and underwent AHCT at Mayo Clinic from 2019 to 2024 were retrospectively recruited. Patients who required salvage therapy following Ven+HMA were excluded. Post-transplant survival (PTS) and relapse incidence were computed. Results: 55 ND-AML patients (60% male, 49% de novo , median age 69 [38-77]) received Ven+HMA (median cycles 3 [2-11]). ELN 2022 cytogenetic risk at time of diagnosis was non-adverse in 67% of patients, while 33% had adverse karyotype. Common mutations at diagnosis included: K/NRAS (88%), TP53 (26%), RUNX1 (23%), ASXL1 (16%), and IDH1/2 (17%). At the time of AHCT, 98% ( n=54 ) were in CR/CRi or MLFS; ELN cytogenetic risk was non-adverse in 91%, and adverse in 5 (9%) patients. Common mutations included: TP53 (16%), TET2 (18%), SRSF2 (15%), ASXL1 (13%), RUNX1 (18%), and DNMT3A (9%). Donor types included HLA-matched unrelated (75%), haplo-identical (11%), matched related (7%), mismatched unrelated (7%). 58% received fludarabine/melphalan conditioning and 54% GVHD prophylaxis with cyclophosphamide. At a median follow up of 25 months (0.7-68 mo), 20 patients (36%) have died, due to relapse in 10 (18%) cases. 3-year cumulative incidence of non-relapse mortality (NRM) was 17%. Median PTS was not reached (1/2/3-year survival 74%/66%/62%). Univariate analysis identified Karnofsky Performance Score <70% (3 vs. 21 months, p<0.01 ), TP53 (14 vs. 21 months p=0.02 ) and TET2 mutation at time of transplant (11 vs. 21 months , p=0.02 ) as risk factors. Multivariable analysis confirmed the prognostic impact of TP53 (HR 2.8) and TET2 mutations (HR 2.9). Age, adverse karyotype at transplant, and donor type did not impact PTS (p>0.1). 13 patients (24%) experienced post-transplant relapse; 1/2/3-year cumulative incidence of relapse was 10%, 21% and 25%, respectively. ELN-defined adverse karyotype at transplant increased risk of relapse (3 year cumulative incidence 80% vs. 17% for non-adverse , p<0.01 ). Overall, 51% of patients developed GVHD; 54%, 39% and 7% were acute, chronic GVHD and both, respectively. GVHD was protective against relapse (3 year incidence 15% vs. 36% in absence of GVHD [p=0.04]). Conclusions: Ven+HMA frontline treatment is associated with favorable post-transplant outcome in elderly ND-AML (3 year PTS 62%/cumulative incidence of relapse 25%/NRM 17%). TP53 mutation and ELN 2022-defined adverse karyotype at the time of transplant independently predicted PTS and relapse incidence, respectively.

6579 Background: Treatment strategies in chronic myelomonocytic leukemia (CMML) are not standardized and include hydroxyurea (HU) and hypomethylating agents (HMA). In a phase 3 study comparing HU and decitabine, in proliferative CMML, response rates were higher for decitabine (56% vs 31%; p<0.01) but overall survival was similar (p=0.67) between the two groups (Itzykson, R. JCO, 2023. 41:1888). In the current retrospective study, we examined the survival impact of different treatment strategies among 457 Mayo Clinic patients with CMML. Methods: The current study was conducted under institutional review board approved minimum risk protocols allowing retrospective patient data collection and analysis. Diagnostic criteria were according to the International Consensus Classification (Arber et al. Blood 2022. 140:1200). All statistical analyses were conducted using JMP 17 software. For survival analysis, patients were censored at time of allogeneic stem cell transplant (ASCT). Results: A total of 457 patients were considered (median age 72 years; 68% males). 209 patients received CMML-directed therapy: HU (N=102), HMA (N=78; azacitidine 32 and decitabine 46). Responses were adjudicated separately for leukocytosis and anemia; normalization of leukocyte count was achieved in 21% vs. 16 % (p<0.01) for HU vs. HMA and overall response in anemia in 1% vs. 9% (p=0.02), respectively. Overall survival did not appear to be impacted by different treatment strategies at any stage of CMML; (i) treated vs. untreated (p=0.3), (ii) HU vs. HMA for first-line therapy (p=0.3), and (iii) HU/HMAs vs. other drugs as first-line therapy (p=0.1). Blast transformation-free survival (BTFS) was also similar between HU vs. HMA as well as HU/HMA vs. other drugs. In univariate analysis, BTFS was inferior in patients receiving CMML-directed therapy (p<0.01); the particular association (HR 2; 95% CI 1.2-3.3) retained its significance in multivariable analysis that also included other risk factors for BTFS: bone marrow blast ≥10% (HR 4.3), circulating blast ≥2% (HR 2.7), WBC ≥13 x 10 9 /L (HR 1.8), and ASXL1 mutation (HR 1.7). Conclusions: In the current retrospective study that included a large number of patients with CMML, chemotherapy with HU or HMA did not appear to affect overall survival but might have increased the risk of blast transformation. The study also suggests superiority of HU for the treatment of leukocytosis and HMA for anemia. Predictors of blast transformation-free survival (BTFS) in 457 patients diagnosed with chronic myelomonocytic leukemia (CMML). BTFS Univariable analysis p-value (HR) Multivariable analysis p-value (HR) CMML-directed therapy <0.01 (2.9; 1.8-4.7) <0.01 (2; 1.2-3.3) Bone marrow blasts ≥10% <0.01 (12.4) 0.01 (4.3) Circulating blasts ≥2% <0.01 (5.2) <0.01 (2.7) WBC ≥13 x 10 9 /L <0.01 (2.9) 0.02 (1.8) ASXL1 mut <0.01 (2.1) 0.02 (1.7)

e18596 Background: The International Consensus (ICC), but not the 5 th edition of the WHO classification (WHO5), distinguishes mature from immature mast cell leukemia (MCL) and systemic mastocytosis (SM) associated with myeloid neoplasm (SM-AMN) from SM associated with myeloid or lymphoid neoplasm (SM-AHN). The objectives of the current study were i) to assess prognostic input from disease classification by ICC vs. WHO5, and ii) to compare the predictive performance of the Mayo Alliance Prognostic scoring (MAPS) with other prognostic models and its prognostic interaction with the ICC-based morphologic classification. Methods: Study patients met diagnostic criteria per ICC/WHO5. MAPS risk variables included i) age >60 years, ii) hemoglobin below sex-adjusted lower limit of normal, iii) platelets <150 × 10⁹/L, iv) alkaline phosphatase above upper limit of normal, and v) advanced, including MCL, SM-AMN, and aggressive (ASM) vs. indolent/smoldering (ISM/SSM) SM. ICC-defined MCL includes only MCL-immature whereas WHO-defined MCL includes both MCL-immature and MCL-mature. WHO-defined SM-AHN includes SM-AMN and SM associated with lymphoid neoplasm (SM-ALN). Results: 910 Mayo Clinic patients with SM were diagnosed between 1968 and 2024 (median age 56 years). ICC categories were ISM/SSM (N=552), ASM (N=115), SM-AMN (N=235), and MCL (N=8). At median follow-up of 4 years, 345 (38%) deaths and 35 (3.8%) leukemic transformations were documented. Overall survival (OS) predictive performance at 5 years was superior with ICC (AUC 0.85), compared to WHO5 (AUC 0.83); median survival was 24.3 years in ISM/SSM, 5.8 years for ASM, 2.0 years for SM-AMN, 2.3 years for SM-AHN, 1.8 years for MCL-mature and 0.08 years for MCL-immature; the difference in OS was significant between MCL-immature and SM-AMN (p<0.01) but not between MCL-mature and SM-AHN (p=0.3). Similarly, OS was similar between MCL-mature and ASM (p=0.8) and between SM-ALN and ASM (p=0.08) but different between MCL-immature and ASM (p<0.01), SM-AMN and ASM (p<0.01), and MCL-mature and MCL-immature (p<0.01). Predictive performance at 5 years was superior with MAPS (AUC 0.91) and MAPS-molecular (AUC 0.91), compared to the mutation-adjusted risk score (MARS; AUC 0.82). Median OS estimates were not reached, 24.2, 11.7, 5.7, 2.6, and 0.7 years, in the presence of 0, 1, 2, 3, 4, or 5 of the forementioned MAPS risk factors. Among informative cases, ASXL1 mutation was the only genetic risk factor with MAPS-independent prognostic relevance. Prognostic inter-independence between ICC and MAPS was confirmed by multivariable analysis. Conclusions: The current study confirms the superior performance of MAPS, in regard to survival prediction, with little additional contribution from mutations. SM sub-classification by the ICC is prognostically independent of MAPS and more valuable than classification by WHO5.

e18590 Background: TP53 mutations ( TP53 MUT ) are known to be associated with adverse prognosis in acute myeloid leukemia (AML) and multihit TP53 MUT in myelodysplastic syndromes (MDS). The prognostic relevance of multihit TP53 MUT in myeloproliferative neoplasms (MPN) was recently highlighted. The current study illustrates survival comparisons in multihit TP53- mutated MPN vs. AML and analysis of associated risk factors. Methods: A Mayo Clinic enterprise-wide database search identified 61 MPN and 81 AML cases with multihit TP53 MUT . Conventional statistical methods were used for analyses. Results: 142 patients with multihit TP53 MUT were included: i) chronic phase MPN (MPN-CP; N=19), ii) accelerated phase MPN (MPN-AP; N=14), iii) blast phase MPN (MPN-BP; N=28) and iv) AML, not including MPN-BP (N=81). Concomitant ASXL1 MUT , EZH2 MUT , IDH1 MUT and IDH2 MUT were more common in MPN-BP, compared to AML. At a median follow up of 0.6 years, 124 (87%) deaths and 19 (13%) allogeneic stem cell transplantations (ASCT) were documented. Overall survival (OS), calculated from time of TP53 MUT detection was similar between MPN-BP (median 4.6 months) and MPN-AP (5.6 months; p=0.5). OS in MPN-BP/AP (median 4.8 months) was inferior to that of AML (median 7.4 months; p=0.04) while that of MPN-CP (median 11.6 months) was similar to AML (0.07) but superior to that of MPN-BP/AP (p<0.01). Age-adjusted multivariable analysis (MVA) confirmed the independent prognostic significance of undergoing ASCT (HR 0.4, p=0.03), MPN-CP or achieving response to pre-transplant therapy (HR 0.2, p<0.01), and concurrent TET2 MUT or DNMT3A MUT (HR 2.7, p<0.01) on OS. Based on these risk factors, a 3-tiered risk model was constructed: low (no risk factors; N=18; median OS 23.8 months); intermediate (1 risk factor; N=44; median 11.1 months); and high (2 or more risk factors; N=80; median 4 months; p<0.01). Comparative analysis of risk factors among distinct diseases confirmed the prognostic significance of ASCT (HR 0.3, p=0.03), achieving response to pre-transplant therapy (0.4, p<0.01) and concurrent TET2 MUT or DNMT3A MUT (HR 5.0, p<0.01) in AML. In MPN AP/BP, OS was influenced by having received chemotherapy vs. supportive care (HR 0.1; p<0.01) and achieving response to pre-transplant therapy (0.2, p<0.01). No significant risk factors for OS were identified in MPN-CP. In MVA, ASCT did not appear to influence OS in MPN AP/BP (p=0.7) and MPN-CP (p=0.4) but the number of informative cases was too low to make definitive conclusions. Conclusions: The current study highlights the equally detrimental impact of multihit TP53 MUT in securing long-term survival in MPN and AML. Short-term survival was positively influenced by ASCT, at least in AML, and disease stage or remission status at time of mutation detection and ASCT, respectively.

e18600 Background: Recent studies have suggested that basophilia in myeloproliferative neoplasms (MPN), in general, and in primary myelofibrosis (PMF), in particular, might be associated with poor prognosis. In the current study, we examined for clinical and genotype correlates as well as the prognostic impact of absolute eosinophil (AEC) and basophil (ABC) counts in essential thrombocythemia (ET) and polycythemia vera (PV). Methods: Diagnostic criteria were according to the International Consensus Classification. Study patients were selected based on the availability of information on AEC and ABC. Institutional reference range for AEC was 0.03 to 0.48 x 10 9 /L and for ABC 0.01 to 0.08 x 10 9 /L. "Eosinophilia" was defined as an AEC of ≥0.5 x 10 9 /L. "Basophilia" was evaluated both at an ABC of ≥0.1 x 10 9 /L and ABC of ≥0.3 x 10 9 /L, the latter representing 3 x the upper limit of the normal reference range. Results: Essential thrombocythemia 660 patients were considered. Median (range) values for AEC and ABC were 0.2 x 10 9 /L (0-2.8) and 0.07 x 10 9 /L (0-1.7), respectively. On univariate analysis, AEC and ABC, as continuous variables, were predictive of inferior overall (OS; p<0.01 for both) but not leukemia-free (LFS), myelofibrosis-free (MFFS), venous thrombosis-free (VTFS), or arterial thrombosis-free (ATFS) survival. In univariable analysis, AEC ≥0.5 x 10⁹/L and ABC ≥0.1 x 10⁹/L negatively impacted OS (p<0.01 for both); significance was sustained during multivariate analysis that included IPSET risk variables: AEC ≥0.5 x 10⁹/L (p<0.01; HR 1.9) and ABC ≥0.1 x 10 9 /L (p<0.01; HR 1.7). Polycythemia vera 478 patients were considered. Median (range) values for AEC and ABC were 0.27 x 10 9 /L (0-6.5) and 0.12 x 10 9 /L (0-3.2), respectively. In univariable analysis, neither AEC nor ABC, as continuous variables were predictive of OS, LFS, MFFS, VTFS, or ATFS. AEC ≥0.5 x 10⁹/L also did not have any impact on disease progression or thromboses. However, ABC ≥0.1 x 10 9 /L was associated with a lower risk of post-diagnosis arterial thrombosis (p=0.03; HR 0.6), and ABC ≥0.3 x 10 9 /L was predictive of inferior LFS (p<0.01; HR 6.5) and MFFS (p<0.01; HR 2.5). ABC ≥0.3 x 10 9 /L sustained prognostic relevance in LFS (p<0.01; HR 7.6) during multivariable analysis that included leukocytosis, platelet count, basophil percentage, age, and palpable splenomegaly. Similar findings were noted with regards to MFFS for ABC ≥0.3 x 10 9 /L (p=0.01; HR 2.3) when compared against palpable splenomegaly and age. Conclusions: The current study suggests that AEC ≥0.5 x 10 9 /L and ABC ≥0.1 x 10 9 /L in ET are independently associated with shortened overall survival, while basophilia (ABC ≥0.3 x 10 9 /L) in PV is an independent predictor of leukemic and myelofibrotic disease progression.

ABSTRACTPolycythemia vera (PV) is invariably associated with a JAK2 mutation, with over 50% of patients harboring additional non‐JAK2 mutations. In the current study, 319 patients with PV underwent NGS at diagnosis or in chronic phase PV (Group A: N = 270, 85%) or at the time of fibrotic (Group B; N = 37, 12%) or leukemic (Group C; N = 12, 4%) transformation. Mutational frequencies involving TP53/SRSF2/IDH1/U2AF1 were significantly (p < 0.05) different between patients in the mutually exclusive Groups A (2%/4%/2%/0.4%), B (8%/0%/0%/5%), and C (50%/25%/17%/8%). Analyses on phenotype/genotype associations and prognostic impact on overall (OS), leukemia‐free (LFS), and myelofibrosis‐free (MFFS) survival were limited to Group A patients. ASXL1MUT was associated with younger age (p < 0.01), SRSF2MUT with older age and leukocytosis (p < 0.01), and TP53MUT with leukocytosis (p < 0.01). Mutation co‐segregation was apparent between ASXL1 and IDH2 (p < 0.01) or SRSF2 (p < 0.01), SRSF2 and IDH2 (p < 0.01), and TP53 and NRAS (p = 0.01). Multivariable analysis identified SRSF2MUT (p < 0.01; HR, 4.2, 1.9–9.5), IDH2MUT (p = 0.01; HR, 5.3, 1.8–15.3), ASXL1MUT (p = 0.04; HR, 2.0, 1.1–3.7), leukocyte count ≥ 15 × 109/L (p < 0.01; HR 2.0, 1.3–3.1), and advanced age (p < 0.01) as risk factors for OS. Median OS in the presence (N = 235; 87%) or absence (N = 35; 13%) of any adverse mutation (i.e., SRSF2MUT, ASXL1MUT, or IDH2MUT) was 8.8 versus 17.8 years (p = 0.01; HR 1.8, 1.1–2.9). In addition, ASXL1MUT (p = 0.02; HR, 1.6–24.9), SRSF2MUT (p = 0.06; HR, 11.9, 1.1–126.2), and advanced age (p = 0.04) were associated with inferior LFS, and SRSF2MUT (p < 0.01; HR, 24.0, 5.5–103.8) and abnormal karyotype (p < 0.01; HR 3.8, 1.6–8.9) with inferior MFFS. The number of non‐JAK2 mutations was significant in predicting outcome in univariate but not multivariable analysis. The observations from the current study highlight the prognostic significance of non‐JAK2 mutations in PV and the prospect of their inclusion in future prognostic models.

We sought to develop a survival model in chronic myelomonocytic leukemia (CMML) that is primarily based on clinical variables and examine additional impact from mutations and karyotype. 457 molecularly-annotated patients were considered. Multivariable analysis identified circulating Blasts ≥2% (1 point), Leukocytes ≥13 x 109/L (1 point), and severe (2 points) or moderate (1 point) Anemia as preferred risk variables in developing a clinical risk Stratification Tool for overall survival (OS), acronymized to "BLAST": low-risk (0 points; median 63 months); intermediate-risk (1 point; median 28 months; HR 2.2, 95% CI 1.6-3.0), and high-risk (2-4 points; median 13 months; 5.4, 4.1-7.3); the corresponding 3/5 year OS rates were 68%/53%, 43%/18%, and 12%/1%. BLAST model performance (AUC 0.77/0.85 at 3/5-years) was shown to be comparable to that of the molecular CMML-specific prognostic scoring system (CMML-mol; AUC 0.73/0.75) and the international prognostic scoring system-molecular (IPSS-M; AUC 0.73/0.74). Multivariable analysis of mutations and karyotype identified PHF6MUT and TET2MUT as being "favorable" and DNMT3AMUT, U2AF1MUT, BCORMUT, SETBP1MUT, ASXL1MUT, NRASMUT, PTPN11MUT, RUNX1MUT, TP53MUT, and adverse karyotype, "unfavorable". Molecular information was subsequently encoded in a combined clinical-molecular risk model (BLAST-mol; AUC 0.80/0.86 at 3/5-years) that included the aforementioned BLAST clinical risk variables and a 3-tiered molecular risk score. BLAST and BLAST-mol were subsequently validated by two separate external cohorts. Independent risk factors for blast transformation included DNMT3AMUT, ASXL1MUT, PHF6WT, leukocytes ≥13 x 109/L, and ≥2% circulating or ≥10% bone marrow blasts. The current study proposes an easy to implement, globally applicable, and molecularly adaptive risk model for CMML.

ABSTRACTA total of 142 patients with myeloproliferative neoplasms (MPNs) or acute myeloid leukemia (AML) associated with multihit TP53 mutations (mTP53 MUT) were accessed from the Mayo Clinic database and included (i) chronic phase MPN (MPN‐CP; N = 19), (ii) accelerated phase MPN (MPN‐AP; N = 14), (iii) blast phase MPN (MPN‐BP; N = 28), and (iv) AML (N = 81). Concurrent ASXL1 MUT, EZH2 MUT, IDH1,MUT and IDH2 MUT were more common in MPN‐MUTBP‐mTP53 compared to AML‐mTP53 MUT. At median of 11.6 months follow‐up, 124 (87%) deaths and 19 (13%) allogeneic stem cell transplantations (ASCT) were documented. Overall survival (OS), calculated from the time of mTP53 MUT detection, was similar between MPN‐BP‐mTP53 MUT (median 4.6 months) and MPN‐AP‐mTP53 MUT (5.6 months; p = 0.5) but both were inferior to MPN‐CP‐mTP53 MUT (11.6 months, p < 0.01). OS in MPN‐CP‐mTP53 MUT was similar to that of AML‐mTP53 MUT (median 7.4 months, p = 0.07). In multivariable analysis, OS was favorably affected by ASCT (HR 0.4, p = 0.03) and disease stage (i.e., chronic phase disease) or achieving response to pre‐transplant chemotherapy (HR 0.2, p < 0.01) and unfavorably by the presence of concurrent TET2 MUT or DNMT3A MUT (HR 2.7, p < 0.01). Based on these risk factors, a 3‐tiered risk model was constructed: low (no risk factors; N = 18; median OS 23.8 months); intermediate (one risk factor; N = 44; 11.1 months); and high (two or more risk factors; N = 80; 4 months; p < 0.01). The current study highlights the equally detrimental impact of mTP53 MUT on long‐term survival in MPN and AML and identifies predictors of short‐term survival.

ABSTRACT The clinical relevance of TP53 mutations ( TP53 MUT ) in myeloproliferative neoplasms (MPN) and their prognostic interaction with MPN subtype designation has not been systematically studied. In the current study, 114 patients with MPN harboring TP53 MUT (VAF ≥ 2%) were evaluated for overall survival (OS), calculated from the time of TP53 MUT detection: chronic phase myelofibrosis (MF‐CP; N = 61); blast‐phase (MPN‐BP; N = 31) or accelerated‐phase (MPN‐AP; N = 16) MPN, and polycythemia vera/essential thrombocythemia (PV/ET; N = 6). Sixty‐five (57%) patients harbored International Consensus Classification (ICC)‐defined multihit TP53 MUT and 56 (49%) monosomal/complex karyotype (MK/CK). Majority of MPN‐BP (90%) and MPN‐AP (81%) while 39% of MF‐CP and none of PV/ET patients harbored multihit TP53 MUT . OS in MPN‐BP and MPN‐AP was equally dismal (median 6 vs. 4.5 months, respectively; p = 1.0), regardless of multihit configuration ( p = 0.44), while OS in TP53 MUT MPN‐BP/AP ( N = 47; median 4 months) was inferior to that of a separate cohort ( N = 49) with TP53 wild‐type MPN‐BP/AP (median 11 months; p < 0.01). OS in MF‐CP was significantly shorter with multihit versus non‐multihit TP53 MUT (median 10 vs. 35 months; HR 2.9; p < 0.01), independent of other MF‐relevant genetic risk factors, including ASXL1/SRSF2/U2AF1 mutations. Multihit TP53 MUT was also associated with inferior survival following allogeneic stem cell transplant (ASCT): median 9 months versus “not reached” in patients with ( N = 9) versus without ( N = 8) multihit TP53 MUT ( p < 0.01). The presence of multihit or non‐multihit TP53 MUT in MPN‐BP/AP or multihit TP53 MUT in MF‐CP is associated with exceptionally poor prognosis and justifies inclusion into the ICC category of “myeloid neoplasms with mutated TP53 .” By contrast, detection of non‐multihit TP53 MUT , by itself, might not endanger short‐term survival in MF‐CP, PV, or ET.