In myelodysplastic syndromes (MDS), deletions of chromosome 7 or 7q are common and correlate with a poor prognosis. The relevant genes on chromosome 7 are unknown. We report here that EZH2, located at 7q36.1, is frequently targeted in MDS. Analysis of EZH2 deletions, missense and frameshift mutations strongly suggests that EZH2 is a tumor suppressor. As EZH2 functions as a histone methyltransferase, abnormal histone modification may contribute to epigenetic deregulation in MDS.

Quantification of residual disease by real-time polymerase chain reaction (PCR) will become a pivotal tool in the development of patient-directed therapy. In recent years, various protocols to quantify minimal residual disease in leukemia or lymphoma patients have been developed. These assays assume that PCR efficiencies are equal for all samples. Determining t(14;18) and albumin reaction efficiencies for sixteen follicular lymphoma patient samples revealed higher efficiencies for blood samples than for lymph node samples in general. However, within one sample both reactions had equivalent efficiencies. Differences in amplification efficiencies between patient samples (low efficiencies) and the calibrator in quantitative analyses result in the underestimation of residual disease in patient samples whereby the weakest positive patient samples are at highest error. Based on these findings for patient samples, the efficiency compensation control was developed. This control includes two reference reactions in a multiplex setting, specific for the beta-actin and albumin housekeeping genes that are present in a constant ratio within DNA templates. The difference in threshold cycle values for both reference reactions, ie, the Ct(2) value, is dependent on the amplification efficiency, and is used to compensate for efficiency differences between patient samples and the calibrator. The beta-actin reference reaction is also used to normalize for DNA input. Furthermore, the efficiency compensation control facilitates identification of patient samples that are so contaminated with PCR inhibitory compounds that different amplification reactions are affected to a different extent. Accurate quantitation of residual disease in these samples is therefore impossible with the current quantitative real-time PCR protocols. Identification and exclusion of these inadequate samples will be of utmost importance in quantitative retrospective studies, but even more so, in future molecular diagnostic analyses.

We assessed the prognostic impact of TET2 mutations and mRNA expression in a prospective cohort of 357 adult AML patients < 60 years of age enrolled in the European Organization For Research and Treatment of Cancer (EORTC)/Gruppo Italiano Malattie Ematologiche dell' Adulto (GIMEMA) AML-12 06991 clinical trial. In addition the co-occurrence with other genetic defects and the functional consequences of TET2 mutations were investigated. TET2 mutations occurred in 7.6 % of the patients and were an independent marker of poor prognosis (p = 0.024). TET2 and IDH1/2 mutations strongly associated with aberrations in the DNA methyltransferase DNMT3A. Functional studies confirmed previous work that neither nonsense truncations, nor missense TET2 mutations, induced 5-hydroxymethylcytosine formation. In addition, we now show that mutant TET2 forms did not act in a dominant negative manner when co-expressed with the wild-type protein. Finally, as loss-of-function TET2 mutations predicted poor outcome, we questioned whether low TET2 mRNA expression in cases of AML without TET2 mutations would affect overall survival. Notably, also AML patients with low TET2 mRNA expression levels showed inferior overall survival.

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Postinduction BCL2/IgH major break point status in BM/PB is not useful for decisions on subsequent therapy for patients with relapsed/resistant FL.

Summary(De-)regulation of apoptosis plays an important role in normal and malignant lymphopoiesis. Apoptosis-regulating genes of the BCL-2 family and the recently identified inhibitors of apoptosis (IAP) family have been implicated in different types of non-Hodgkin lymphoma (NHL). To investigate whether expression of specific apoptosis-regulating genes correlated with different types of lymphoid malignancies, we measured the expression of five BCL-2 family genes, four IAP family genes and SMAC by real-time quantitative polymerase chain reaction in patient samples. In total, 137 samples from B-and T-cell acute lymphoblastic leukaemia (ALL), B-cell chronic lymphocytic leukaemia (CLL), six different NHL types and three control tissue types were analysed. The data were further analysed using cluster and discriminant analysis. Three specific expression patterns were identified for CLL, ALL and NHL respectively. CLL samples, as well as B-ALL and follicular lymphoma samples showed high similarity in the expression of these apoptosis-regulating genes and could be distinguished from each other and other diseases and controls. Discriminant analysis identified three members of the IAP family, C-IAP1, C-IAP2 and SURVIVIN, as the most informative genes to discriminate between these lymphoid malignancies.

Summary. We have designed a real-time CBFB-MYH11 reverse transcription polymerase chain reaction (RT-PCR) assay to quantify minimal residual disease (MRD) in patients with inv(16)-positive acute myeloid leukaemia (AML). Six patients were followed for a median of 17AE5 months after diagnosis during which 120 evaluable samples were analysed. The CBFB-MYH11 expression at diagnosis varied only fourfold between the six patients and was virtually identical to that observed in the CBFB-MYH11-positive cell line ME-1. For two cases, a patient-specific real-time PCR for CBFB-MYH11 quantification at genomic DNA level was designed. Similar disease levels were found at the RNA and genomic DNA level during and after treatment, indicating that CBFB-MYH11 gene expression was unaltered during treatment and that the percentage of malignant cells can be accurately quantified at the RNA level. Following successive courses of chemotherapy, the reduction of malignant cells was found to be significantly more pronounced (80-250-fold greater) in peripheral blood compared with bone marrow in five out of six cases tested. Treatment with gemtuzumab ozogamicin as sole agent at relapse did not result in a selective decrease of tumour cells in three cases analysed. We conclude that real-time PCR is a powerful method of monitoring MRD levels and quantifying the antileukaemic effect of separate (experimental) courses of chemotherapy.

Aberrations in protein ubiquitination have recently been identified in the pathogenesis of acute myeloid leukemia (AML). We studied whether expression changes of more than 1600 ubiquitination related genes correlated with clinical outcome in 525 adult AML patients. High expression of one of these genes, BRE, was observed in 3% of the cases and predicted favorable prognosis independently of known prognostic factors (5-year overall survival: 57%). Remarkably, unsupervised expression profiling showed that 86% of high BREexpressing patients were confined to a previously unrecognized cluster. High