Interferon-␣ (IFN-␣) is a nonleukemogenic treatment of polycythemia vera (PV

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Drug-induced cleavage of DNA by topoisomerase II mediates the formation of chromosomal translocation breakpoints in mitoxantrone-related APL and in APL that occurs after therapy with other topoisomerase II poisons.

Abstract. The immunosuppressive drug tacrolimus, whose pharmacokinetic characteristics display large interindividual variations, is a substrate for P-glycoprotein (P-gp), the product of the multidrug resistance-1 (MDR1) gene. Some of the single nucleotide polymorphisms (SNP) of MDR1 reported correlated with the in vivo activity of P-gp. Because P-gp is known to control tacrolimus intestinal absorption, it was postulated that these polymorphisms are associated with tacrolimus pharmacokinetic variations in renal transplant recipients. The objective of this study was to evaluate in a retrospective study of 81 renal transplant recipients the effect on tacrolimus dosages and concentration/dose ratio of four frequent MDR1 SNP possibly associated with P-gp function (T-129C in exon 1b, 1236CϾT in exon 12, 2677GϾT,A in exon 21, and 3435CϾT in exon 26). As in the general population, the SNP in exons 12, 21, and 26 were frequent (16, 17.3, and 22.2% for the variant homozygous genotype, respectively) and exhibited incomplete linkage disequilibrium. One month after tacrolimus introduction, exon 21 SNP correlated significantly with the daily tacrolimus dose (P Յ 0.05) and the concentration/dose ratio (P Յ 0.02). Tacrolimus dose requirements were 40% higher in homozygous than wild-type patients for this SNP. The concentration/dose ratio was 36% lower in the wild-type patients, suggesting that, for a given dose, their tacrolimus blood concentration is lower. Haplotype analysis substantiated these results and suggested that exons 26 and 21 SNP may be associated with tacrolimus dose requirements. Genotype monitoring of the MDR1 gene reliably predicts the optimal dose of tacrolimus in renal transplant recipients and may predict the initial daily dose needed by individual patients to obtain adequate immunosuppression.

Determination of CYP3A5 genotype is predictive of the dose of tacrolimus in renal transplant recipients and may help to determine the initial daily dose needed by individual patients for adequate immunosuppression without excess nephrotoxicity.

Juvenile myelomonocytic leukemia (JMML) is a rare and severe myelodysplastic and myeloproliferative neoplasm of early childhood initiated by germline or somatic RAS-activating mutations. Genetic profiling and whole-exome sequencing of a large JMML cohort (118 and 30 cases, respectively) uncovered additional genetic abnormalities in 56 cases (47%). Somatic events were rare (0.38 events/Mb/case) and restricted to sporadic (49/78; 63%) or neurofibromatosis type 1 (NF1)-associated (8/8; 100%) JMML cases. Multiple concomitant genetic hits targeting the RAS pathway were identified in 13 of 78 cases (17%), disproving the concept of mutually exclusive RAS pathway mutations and defining new pathways activated in JMML involving phosphoinositide 3-kinase (PI3K) and the mTORC2 complex through RAC2 mutation. Furthermore, this study highlights PRC2 loss (26/78; 33% of sporadic JMML cases) that switches the methylation/acetylation status of lysine 27 of histone H3 in JMML cases with altered RAS and PRC2 pathways. Finally, the association between JMML outcome and mutational profile suggests a dose-dependent effect for RAS pathway activation, distinguishing very aggressive JMML rapidly progressing to acute myeloid leukemia.

V617F JAK2 mutation is a reliable molecular marker of polycythemia vera (PV), potentially useful to monitor the effect of treatments in this disease. In a phase 2 study of pegylated (peg) IFN-␣-2a in PV, we performed prospective sequential quantitative evaluation of the percentage of mutated JAK2 allele (%V617F) by realtime polymerase chain reaction (PCR). The %V617F decreased in 24 (89%) of 27 treated patients, from a mean of 49% to a mean of 27% (mean decrease of 44%; P < .001), and no evidence for a plateau was observed. In one patient, mutant JAK2 was no longer detectable after 12 months. In 3 patients homozygous for the mutation, reappearance of 50% of wildtype allele was observed during treatment. The results seem to confirm the hypothesis that IFN-␣ preferentially targets the malignant clone in PV and show that %V617F assessment using a quantitative method may provide the first tool to monitor minimal residual disease in PV. This trial was registered at www. clinicaltrials.gov as #NCT00241241. (Blood.

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