Robert Kralovics

Deletions of the transcription factor Ikaros in myeloproliferative neoplasms.

Transformation to acute leukemia is a major complication of myeloproliferative neoplasms (MPNs), however, the genetic changes leading to transformation remain largely unknown. We screened nine patients with post-MPN leukemia for chromosomal aberrations using microarray karyotyping. Deletions on the short arm of chromosome 7 (del7p) emerged as a recurrent defect. We mapped the common deleted region to the IKZF1 gene, which encodes the transcription factor Ikaros. We further examined the frequency of IKZF1 deletions in a total of 29 post-MPN leukemia and 526 MPN patients without transformation and observed a strong association of IKZF1 deletions with post-MPN leukemia in two independent cohorts. Patients with IKZF1 loss showed complex karyotypes, and del7p was a late event in the genetic evolution of the MPN clone. IKZF1 deletions were observed in both undifferentiated and differentiated myeloid cell types, indicating that IKZF1 loss does not cause differentiation arrest but rather renders progenitors susceptible to transformation, most likely through chromosomal instability. Induced Ikzf1 haploinsufficiency in primary murine progenitors resulted in elevated Stat5 phosphorylation and increased cytokine-dependent growth, suggesting that reduced expression of IKZF1 is sufficient to perturb growth regulation. Thus, IKZF1 loss is an important step in the leukemic transformation of a subpopulation of MPN patients.

Rare germline variants in regions of loss of heterozygosity may influence clinical course of hematological malignancies

Rare germline variants in regions of loss of heterozygosity may influence clinical course of hematological malignancies

Low-burden TP53 mutations in chronic phase of myeloproliferative neoplasms: association with age, hydroxyurea administration, disease type and JAK2 mutational status

The multistep process of TP53 mutation expansion during myeloproliferative neoplasm (MPN) transformation into acute myeloid leukemia (AML) has been documented retrospectively. It is currently unknown how common TP53 mutations with low variant allele frequency (VAF) are, whether they are linked to hydroxyurea (HU) cytoreduction, and what disease progression risk they carry. Using ultra-deep next-generation sequencing, we examined 254 MPN patients treated with HU, interferon alpha-2a or anagrelide and 85 untreated patients. We found TP53 mutations in 50 cases (0.2–16.3% VAF), regardless of disease subtype, driver gene status and cytoreduction. Both therapy and TP53 mutations were strongly associated with older age. Over-time analysis showed that the mutations may be undetectable at diagnosis and slowly increase during disease course. Although three patients with TP53 mutations progressed to TP53-mutated or TP53-wild-type AML, we did not observe a significant age-independent impact on overall survival during the follow-up. Further, we showed that complete p53 inactivation alone led to neither blast transformation nor HU resistance. Altogether, we revealed patients age as the strongest factor affecting low-burden TP53 mutation incidence in MPN and found no significant age-independent association between TP53 mutations and hydroxyurea. Mutations may persist at low levels for years without an immediate risk of progression.