Nicole Naumann

Additional mutations in SRSF2, ASXL1 and/or RUNX1 identify a high-risk group of patients with KIT D816V(+) advanced systemic mastocytosis

Most patients with KIT D816V+ advanced systemic mastocytosis (SM) are characterized by somatic mutations in additional genes. We sought to clarify the prognostic impact of such mutations. Genotype and clinical characteristics of 70 multi-mutated KIT D816V+ advanced SM patients were included in univariate and multivariate analyses. The most frequently identified mutated genes were TET2 (n=33 of 70 patients), SRSF2 (n=30), ASXL1 (n=20), RUNX1 (n=16) and JAK2 (n=11). In univariate analysis, overall survival (OS) was adversely influenced by mutations in SRSF2 (P<0.0001), ASXL1 (P=0.002) and RUNX1 (P=0.03), but was not influenced by mutations in TET2 or JAK2. In multivariate analysis, SRSF2 and ASXL1 remained the most predictive adverse indicators concerning OS. Furthermore, we found that inferior OS and adverse clinical characteristics were significantly influenced by the number of mutated genes in the SRSF2/ASXL1/RUNX1 (S/A/R) panel (P<0.0001). In conclusion, the presence and number of mutated genes within the S/A/R panel are adversely associated with advanced disease and poor survival in KIT D816V+ SM. On the basis of these findings, inclusion of molecular markers should be considered in upcoming prognostic scoring systems for patients with SM.

Molecular profiling of myeloid progenitor cells in multi-mutated advanced systemic mastocytosis identifies KIT D816V as a distinct and late event

To explore the molecular profile and its prognostic implication in systemic mastocytosis (SM), we analyzed the mutation status of granulocyte–macrophage colony-forming progenitor cells (CFU-GM) in patients with KIT D816V+ indolent SM (ISM, n=4), smoldering SM (SSM, n=2), aggressive SM (ASM, n=1), SM with associated clonal hematologic non-mast cell lineage disorder (SM-AHNMD, n=5) and ASM-AHNMD (n=7). All patients with (A)SM-AHNMD (n=12) carried 1–4 (median 3) additional mutations in 11 genes tested, most frequently TET2, SRSF2, ASXL1, CBL and EZH2. In multi-mutated (A)SM-AHNMD, KIT D816V+ single-cell-derived CFU-GM colonies were identified in 8/12 patients (median 60%, range 0–95). Additional mutations were identified in CFU-GM colonies in all patients, and logical hierarchy analysis indicated that mutations in TET2, SRSF2 and ASXL1 preceded KIT D816V. In ISM/SSM, no additional mutations were detected and CFU-GM colonies were exclusively KIT D816V−. These data indicate that (a) (A)SM-AHNMD is a multi-mutated neoplasm, (b) mutations in TET2, SRSF2 or ASXL1 precede KIT D816V in ASM-AHNMD, (c) KIT D816V is thus a phenotype modifier toward SM and (d) KIT D816V or other mutations are rare in CFU-GM colonies of ISM/SSM patients, which might explain at least in part their better prognosis.

KIT D816V and JAK2 V617F mutations are seen recurrently in hypereosinophilia of unknown significance

Myeloproliferative neoplasms with eosinophilia are commonly characterized by a normal karyotype and remain poorly defined at the molecular level. We therefore investigated 426 samples from patients with hypereosinophilia of unknown significance initially referred for screening of the FIP1L1‐PDGFRA (FP) fusion gene also for KIT D816V and JAK2 V617F mutations. Overall, 86 (20%) patients tested positive: FP+ in 55 (12%), KIT D816V+ in 14 (3%), and JAK2 V617F+ in 17 (4%) patients, respectively. To gain better insight into clinical characteristics, we compared these cases with 31 additional and well‐characterized KIT D816V+ eosinophilia‐associated systemic mastocytosis (SM‐eo) patients enrolled within the “German Registry on Disorders of Eosinophils and Mast cells.” Significant differences included younger age, male predominance, and higher eosinophil counts for FP+ cases while abdominal lymphadenopathy, ascites, and serum tryptase levels >100 μg/l were characteristic for those with KIT D816V. Leukocytes, hemoglobin, and splenomegaly did not differ significantly. A median of three additional mutations, most frequently TET2 and SRSF2, were identified in 12/13 KIT D816V+ SM‐eo patients with available material indicating a more complex molecular pathogenesis. Median survival was not reached for FP+ cases but was only 26 and 41 months for KIT D816V+ SM and JAK2 V617F+ MPN‐eo, respectively. Eosinophilia of ≥2 × 109/l was identified as discriminator for inferior survival in KIT D816V+ and/or JAK2 V617F+ patients (median survival 20 months vs. not reached, P = 0.002). Thus, there is a clear prognostic and therapeutic rationale for detection of KIT D816V and JAK2 V617F in the diagnostic work up of eosinophilia. Am. J. Hematol. 90:774–777, 2015.

The clinical and molecular diversity of mast cell leukemia with or without associated hematologic neoplasm.

Mast cell leukemia is a rare variant of advanced systemic mastocytosis characterized by at least 20% of mast cells in a bone marrow smear. We evaluated clinical and molecular characteristics of 28 patients with (n=20, 71%) or without an associated hematologic neoplasm. De novo mast cell leukemia was diagnosed in 16 of 28 (57%) patients and secondary mast cell leukemia evolving from other advanced systemic mastocytosis subtypes in 12 of 28 (43%) patients, of which 7 patients progressed while on cytoreductive treatment. Median bone marrow mast cell infiltration was 65% and median serum tryptase was 520 μg/L. C-findings were identified in 26 of 28 (93%) patients. Mutations in KIT (D816V, n=19; D816H/Y, n=5; F522C, n=1) were detected in 25 of 28 (89%) patients and prognostically relevant additional mutations in SRSF2, ASXL1 or RUNX1 (S/A/Rpos) in 13 of 25 (52%) patients. Overall response rate in 18 treatment-naïve patients was 5 of 12 (42%) on midostaurin and 1 of 6 (17%) on cladribine, and after switch 1 of 4 (25%) on midostaurin and 0 of 3 on cladribine, respectively. S/A/Rpos adversely affected response to treatment and progression to secondary mast cell leukemia (n=6) or acute myeloid leukemia (n=3) while on treatment (P<0.05). The median overall survival from mast cell leukemia diagnosis was 17 months as compared to 44 months in a control group of 124 patients with advanced systemic mastocytosis but without mast cell leukemia (P=0.03). In multivariate analyses, S/A/Rpos remained the only independent poor prognostic variable predicting overall survival (P=0.007). In conclusion, the molecular signature should be determined in all patients with mast cell leukemia because of its significant clinical and prognostic relevance.

Response and progression on midostaurin in advanced systemic mastocytosis: KIT D816V and other molecular markers.

In advanced systemic mastocytosis (advSM), disease evolution is often triggered by KIT mutations (D816V in >80% of cases) and by additional mutations (eg, in SRSF2, ASXL1, and/or RUNX1 [S/A/Rpos in >60% of cases]). In a recently reported phase 2 study, midostaurin, a multikinase/KIT inhibitor, demonstrated an overall response rate (ORR) of 60% in advSM but biomarkers predictive of response are lacking. We evaluated the impact of molecular markers at baseline and during follow-up in 38 midostaurin-treated advSM patients. The median overall survival (OS) was 30 months (95% confidence interval, 6-54) from start of midostaurin. ORR and OS were significantly different between S/A/Rneg (n = 12) and S/A/Rpos (n = 23) patients (ORR: 75% vs 39%, P = .04; OS: P = .01, HR 4.5 [1.3-16.2]). Depending on the relative reduction of the KIT D816V expressed allele burden (EAB) at month 6, patients were classified as KIT responders (≥25%, n = 17) or KIT nonresponders (<25%, n = 11). In univariate analyses at month 6, reduction of KIT D816V EAB ≥25%, tryptase ≥50%, and alkaline phosphatase ≥50% were significantly associated with improved OS. In multivariate analysis, only KIT D816V EAB reduction ≥25% remained an independent on-treatment marker for improved OS (P = .004, HR 6.8 [1.8-25.3]). Serial next-generation sequencing analysis of 28 genes in 16 patients revealed acquisition of additional mutations or increasing variant allele frequency in K/NRAS, RUNX1, IDH2, or NPM1 associated with progression in 7 patients. In midostaurin-treated advSM patients, the complexity and dynamics of mutational profiles significantly affect response, progression, and prognosis.

Fusion of PDGFRB to MPRIP, CPSF6, and GOLGB1 in three patients with eosinophilia-associated myeloproliferative neoplasms

In eosinophilia‐associated myeloproliferative neoplasms (MPN‐eo), constitutive activation of protein tyrosine kinases (TK) as consequence of translocations, inversions, or insertions and creation of TK fusion genes is recurrently observed. The most commonly involved TK and their potential TK inhibitors include PDGFRA at 4q12 or PDGFRB at 5q33 (imatinib), FGFR1 at 8p11 (ponatinib), and JAK2 at 9p24 (ruxolitinib). We here report the identification of three new PDGFRB fusion genes in three male MPN‐eo patients: MPRIP‐PDGFRB in a case with t(5;17)(q33;p11), CPSF6‐PDGFRB in a case with t(5;12)(q33;q15), and GOLGB1‐PDGFRB in a case with t(3;5)(q13;q33). The fusion proteins identified by 5′‐rapid amplification of cDNA ends polymerase chain reaction (PCR) or DNA‐based long distance inverse PCR are predicted to contain the TK domain of PDGFRB. The partner genes contain domains like coiled‐coil structures, which are likely to cause dimerization and activation of the TK. In all patients, imatinib induced rapid and durable complete remissions.

Increase of DNA damage and alteration of the DNA damage response in myelodysplastic syndromes and acute myeloid leukemias

Increased DNA damage and alteration of the DNA damage response (DDR) are critical features of genetic instability presumably implicated in pathogenesis of myelodysplastic syndromes (MDS) and acute myeloid leukemias (AML). We used immunofluorescence staining of γH2AX and 53BP1 for analyzing DNA double-strand breaks (DSB) in MDS and AML cell lines, in CD34+ selected cells of normal and MDS bone marrow (including three cases of chronic myelomonocytic leukemias) and in blasts of AML bone marrow. In addition, we screened for activation of the DDR by immunoblotting of p-ATM, p-ATR, p-CHK1, p-CHK2 and p-TP53. As compared to γH2AX foci levels in normal bone marrow samples (0.2 focus per CD34+ cell±0.0; mean±standard error of mean), increased levels of γH2AX foci were detected in 16/16 MDS bone marrow samples (2.8 foci per CD34+ cell±0.5), 18/18 AML bone marrow samples (5.5 foci per blast±0.5), 1/1 MDS cell line (6.4 foci per cell) and 6/6 AML cell lines (12.0 foci per cell±0.6). γH2AX and 53BP1 co-localized in all tested samples forming diffuse, clustered and marginal patterns. Further, DDR proteins were expressed heterogeneously suggesting impairment of the DDR. In summary, our results provide evidence for a continuous increase of DSB across the spectrum from MDS to AML in conjunction with an impaired DDR. Co-localization of γH2AX and 53BP1 indicates promotion of (in)effective nonhomologous end-joining repair mechanisms at sites of DSB. Moreover, γH2AX/53BP1 foci distribution presumably reveals a non-random spatial organization of the genome in MDS and AML.

Cytogenetically cryptic ZMYM2-FLT3 and DIAPH1-PDGFRB gene fusions in myeloid neoplasms with eosinophilia.

Cytogenetically cryptic ZMYM2-FLT3 and DIAPH1-PDGFRB gene fusions in myeloid neoplasms with eosinophilia

Incidence and prognostic impact of cytogenetic aberrations in patients with systemic mastocytosis

The clinical behavior of systemic mastocytosis (SM) is strongly associated with activating mutations in KIT (D816V in >80% of cases), with the severity of the phenotype influenced by additional somatic mutations, for example, in SRSF2, ASXL1, or RUNX1. Complex molecular profiles are frequently associated with the presence of an associated hematologic neoplasm (AHN) and an unfavorable clinical outcome. However, little is known about the incidence and prognostic impact of cytogenetic aberrations. We analyzed cytogenetic and molecular characteristics of 109 patients (KIT D816V+, n = 102, 94%) with indolent (ISM, n = 26) and advanced SM (n = 83) with (n = 73, 88%) or without AHN. An aberrant karyotype was identified in SM‐AHN (16/73, 22%) patients only. In patients with an aberrant karyotype, additional somatic mutations were identified in 12/16 (75%) patients. Seven of 10 (70%) patients with a poor‐risk karyotype, for example, monosomy 7 or complex karyotype, and 1/6 (17%) patients with a good‐risk karyotype progressed to secondary acute myeloid leukemia (n = 7) or mast cell leukemia (n = 1) within a median of 40 months (range 2‐190, P = .04). In advanced SM, the median overall survival (OS) of poor‐risk karyotype patients was significantly shorter than in good‐risk/normal karyotype patients (4 vs 39 months; hazard ratio 11.7, 95% CI 5.0‐27.3; P < .0001). Additionally, the shortened OS in patients with poor‐risk karyotype was independent from the mutation status. In summary, a poor‐risk karyotype is an independent prognostic variable in advanced SM. Cytogenetic and molecular analyses should be routinely performed in all patients with advanced SM ± AHN because these investigations greatly support prognostication and treatment decisions.

Leukocyte DNA damage after reduced and conventional absorbed radiation doses using 3rd generation dual-source CT technology.

Purpose Computed tomography (CT) scans are an important source of ionizing irradiation (IR) in medicine that can induce a variety of DNA damage in human tissues. With technological improvements CT scans at reduced absorbed doses became feasible presumably lowering genotoxic side effects. Materials and methods For measuring DNA damage we performed γH2AX foci microscopy in peripheral blood mononuclear cells (PBMC) after exposure to reduced and conventional absorbed radiation doses using 3rd generation dual-source CT (DSCT) technology. Results CT scans performed at reduced absorbed doses of 3 mGy induced significant lower levels (p < 0.0001) of DNA damage (0.05 focus per cell ± 0.01 [mean ± standard error of mean]) at 5 min after IR compared to conventional absorbed doses of 15 mGy (0.30 focus per cell ± 0.03). With ongoing DNA repair background γH2AX foci levels (0.05 focus per cell) were approached at 24 h after CT with both protocols. Conclusion Our results provide evidence that reduced absorbed doses mediated by adjusted tube current in 3rd generation DSCT induce lower levels of DNA damage in PBMC compared to conventional absorbed doses suggesting a lower genotoxic risk for state-of-the-art tube current reduced CT protocols.