Anaplastic lymphoma kinase (ALK)-positive lymphomas respond to chemotherapy, but relapses, which bear a poor prognosis, occur. Crizotinib inhibits ALK in vitro and in vivo and was administered as monotherapy to 11 ALK+ lymphoma patients who were resistant/refractory to cytotoxic therapy. The overall response rate was 10 of 11 (90.9%; 95% confidence interval [CI] = 58.7% to 99.8%). Disease status at the latest follow-up is as follows: four patients are in complete response (CR) (months >21, >30, >35, >40) under continuous crizotinib administration; 4 patients had progression of disease (months 1, 2, 2, 2); 1 patient obtained CR on crizotinib, received an allogeneic bone marrow transplant, and is in CR; 2 patients (treated before and/or after allogeneic bone marrow transplant) obtained and are still in CR but they have stopped crizotinib. Overall and progression-free survival rates at 2 years are 72.7% (95% CI = 39.1% to 94.0%) and 63.7% (95% CI = 30.8% to 89.1%), respectively. ALK mutations conferring resistance to crizotinib in vitro could be identified in relapsed patients. Crizotinib exerted a potent antitumor activity with durable responses in advanced, heavily pretreated ALK+ lymphoma patients, with a benign safety profile.

Self‐renewal of Bcr‐Abl+ chronic myeloid leukemia (CML) cells is sustained by a nuclear activated serine/threonine‐(S/T) unphosphorylated β‐catenin. Although β‐catenin can be tyrosine (Y)‐phosphorylated, the occurrence and biological relevance of this covalent modification in Bcr‐Abl‐associated leukemogenesis is unknown. Here we show that Bcr‐Abl levels control the degree of β‐catenin protein stabilization by affecting its Y/S/T‐phospho content in CML cells. Bcr‐Abl physically interacts with β‐catenin, and its oncogenic tyrosine kinase activity is required to phosphorylate β‐catenin at Y86 and Y654 residues. This Y‐phospho β‐catenin binds to the TCF4 transcription factor, thus representing a transcriptionally active pool. Imatinib, a Bcr‐Abl antagonist, impairs the β‐catenin/TCF‐related transcription causing a rapid cytosolic retention of Y‐unphosphorylated β‐catenin, which presents an increased binding affinity for the Axin/GSK3β complex. Although Bcr‐Abl does not affect GSK3β autophosphorylation, it prevents, through its effect on β‐catenin Y phosphorylation, Axin/GSK3β binding to β‐catenin and its subsequent S/T phosphorylation. Silencing of β‐catenin by small interfering RNA inhibited proliferation and clonogenicity of Bcr‐Abl+ CML cells, in synergism with Imatinib. These findings indicate the Bcr‐Abl triggered Y phosphorylation of β‐catenin as a new mechanism responsible for its protein stabilization and nuclear signalling activation in CML.

Imatinib is effective for the treatment of chronic myeloid leukemia (CML). However even undetectable BCR‐ABL1 by Q‐RT‐PCR does not equate to eradication of the disease. Digital‐PCR (dPCR), able to detect 1 BCR‐ABL1 positive cell out of 10⁷, has been recently developed. The ISAV study is a multicentre trial aimed at validating dPCR to predict relapses after imatinib discontinuation in CML patients with undetectable Q‐RT‐PCR. CML patients under imatinib therapy since more than 2 years and with undetectable PCR for at least 18 months were eligible. Patients were monitored by standard Q‐RT‐PCR for 36 months. Patients losing molecular remission (two consecutive positive Q‐RT‐PCR with at least 1 BCR‐ABL1/ABL1 value above 0.1%) resumed imatinib. The study enrolled 112 patients, with a median follow‐up of 21.6 months. Fifty‐two of the 108 evaluable patients (48.1%), relapsed; 73.1% relapsed in the first 9 months but 14 late relapses were observed between 10 and 22 months. Among the 56 not‐relapsed patients, 40 (37.0% of total) regained Q‐RT‐PCR positivity but never lost MMR. dPCR results showed a significant negative predictive value ratio of 1.115 [95% CI: 1.013–1.227]. An inverse relationship between patients age and risk of relapse was evident: 95% of patients <45 years relapsed versus 42% in the class ≥45 to <65 years and 33% of patients ≥65 years [P(χ²) < 0.0001]. Relapse rates ranged between 100% (45 years, dPCR‐). Imatinib can be safely discontinued in the setting of continued PCR negativity; age and dPCR results can predict relapse. Am. J. Hematol. 90:910–914, 2015.

Despite the recent identification of recurrent SETBP1 mutations in atypical chronic myeloid leukemia (aCML), a complete description of the somatic lesions responsible for the onset of this disorder is still lacking. To find additional somatic abnormalities in aCML, we performed whole-exome sequencing on 15 aCML cases. In 2 cases (13.3%), we identified somatic missense mutations in the ETNK1 gene. Targeted resequencing on 515 hematological clonal disorders revealed the presence of ETNK1 variants in 6 (8.8%) of 68 aCML and 2 (2.6%) of 77 chronic myelomonocytic leukemia samples. These mutations clustered in a small region of the kinase domain, encoding for H243Y and N244S (1/8 H243Y; 7/8 N244S). They were all heterozygous and present in the dominant clone. The intracellular phosphoethanolamine/phosphocholine ratio was, on average, 5.2-fold lower in ETNK1-mutated samples (P < .05). Similar results were obtained using myeloid TF1 cells transduced with ETNK1 wild type, ETNK1-N244S, and ETNK1-H243Y, where the intracellular phosphoethanolamine/phosphocholine ratio was significantly lower in ETNK1-N244S (0.76 ± 0.07) and ETNK1-H243Y (0.37 ± 0.02) than in ETNK1-WT (1.37 ± 0.32; P = .01 and P = .0008, respectively), suggesting that ETNK1 mutations may inhibit the catalytic activity of the enzyme. In summary, our study shows for the first time the evidence of recurrent somatic ETNK1 mutations in the context of myeloproliferative/myelodysplastic disorders. Key Points Whole-exome sequencing reveals the presence of recurrent somatic mutations of ETNK1 in patients with atypical chronic myeloid leukemia. ETNK1 mutations impair the catalytic activity of the enzyme, causing a decrease in the intracellular levels of phosphoethanolamine.

SETBP1 variants occur as somatic mutations in several hematological malignancies such as atypical chronic myeloid leukemia and as de novo germline mutations in the Schinzel–Giedion syndrome. Here we show that SETBP1 binds to gDNA in AT-rich promoter regions, causing activation of gene expression through recruitment of a HCF1/KMT2A/PHF8 epigenetic complex. Deletion of two AT-hooks abrogates the binding of SETBP1 to gDNA and impairs target gene upregulation. Genes controlled by SETBP1 such as MECOM are significantly upregulated in leukemias containing SETBP1 mutations. Gene ontology analysis of deregulated SETBP1 target genes indicates that they are also key controllers of visceral organ development and brain morphogenesis. In line with these findings, in utero brain electroporation of mutated SETBP1 causes impairment of mouse neurogenesis with a profound delay in neuronal migration. In summary, this work unveils a SETBP1 function that directly affects gene transcription and clarifies the mechanism operating in myeloid malignancies and in the Schinzel–Giedion syndrome caused by SETBP1 mutations.