NG2 Molecule Expression in Acute Lymphoblastic Leukemia B Cells: A Flow-Cytometric Marker for the Rapid Identification of KMT2A Gene Rearrangements.

Background: B-lineage acute lymphoblastic leukemias (B-ALL) harboring rearrangements of the histone lysine [K]-Methyltransferase 2A (KMT2A) gene on chromosome 11q23 (KMT2A-r) represent a category with dismal prognosis. The prompt identification of these cases represents an urgent clinical need. Considering the correlation between rat neuron glial-antigen 2 (NG2) chondroitin-sulfate-proteoglycan molecule expression and KMT2A-r, we aimed to identify an optimized cytofluorimetric diagnostic panel to predict the presence of KMT2A-r. Materials and Methods: We evaluated 88 NG2+ B-ALL cases identified with an NG2 positivity threshold >10% from a cohort of 1382 newly diagnosed B-ALLs referred to the Division of Hematology of 'Sapienza' University of Rome. Results: Eighty-five of 88 (96.6%) NG2+ B-ALLs harbored KMT2A-r and were mainly pro-B ALL (77/85; 91%). Only 2 B-ALLs with KMT2A-r showed NG2 expression below 10%, probably due to the steroid therapy administered prior to cytofluorimetric analysis.Compared to KMT2A-r-cases, KMT2A r+ B-ALLs showed a higher blast percentage, significantly higher mean fluorescence intensity (MFI) of CD45, CD38, and CD58, and significantly lower MFI of CD34, CD22, TdT, and CD123.The study confirmed differences in CD45, CD34, CD22, and TdT MFI within the same immunologic EGIL group (European Group for the immunological classification of leukemias), indicating no influence of the B-ALLs EGIL subtype on the KMT2A-r+ B-ALLs immunophenotype. Conclusions: Our data demonstrate the association between NG2 and KMT2A-r in B-ALLs identify a distinctive immunophenotypic pattern, useful for rapid identification in diagnostic routines of these subtypes of B-ALLs with a poor prognosis that benefits from a specific therapeutic approach.

A multicenter total therapy strategy for de novo adult Philadelphia chromosome positive acute lymphoblastic leukemia patients: final results of the GIMEMA LAL1509 protocol.

The GIMEMA LAL1509 protocol, designed for adult (≥18-60 years) de novo Ph+ acute lymphoblastic leukemia patients, was based on a dasatinib plus steroids induction - with central nervous system prophylaxis - followed by dasatinib alone in patients in complete molecular response or chemotherapy and/or allogeneic transplantation in patients not reaching a complete molecular response. Sixty patients (median age 41.9 years) were enrolled: 33 were p190+, 18 p210+ and 9 p190/p210+. At the end of induction (day +85), 58 patients (97%) achieved a complete hematologic remission. No deaths in induction were recorded. Eleven patients (18.3%) obtained a complete molecular response. Among non-complete molecular responders (n=47), 22 underwent an allogeneic transplant. Seventeen hematologic relapses occurred (median 7 months, range 3-40.1), 13 during consolidation and 4 post-transplant. ABL1 mutations (5 T315I, 3 V299L, 1 E281K and 1 G254E) were found in 10/13 relapsed cases. With a median follow-up of 57.4 months (range: 4.2-75.6), overall survival and disease-free survival are 56.3% and 47.2%. A better diseasefree survival was observed in patients who obtained a molecular response at day +85 compared to cases who did not. The presence of additional copy number aberrations - IKZF1 plus CDKN2A/B and/or PAX5 deletions - was the most important unfavorable prognostic factor on overall and disease-free survival (p=0.005 and p=0.0008). This study shows that in adult Ph+ ALL long-term survivals can be achieved with a total-therapy strategy based on a chemo-free induction and, in complete molecular responders, also without further systemic chemotherapy. Finally, the screening of additional copy number aberrations should be included in the diagnostic work-up. EudraCT 2010-019119-39.

Clinical outcome and monitoring of minimal residual disease in patients with acute lymphoblastic leukemia expressing the MLL/ENL fusion gene.

We analyzed 12 MLL/ENL positive ALL patients consecutively diagnosed between 1999 and 2009. The MLL/ENL fusion was identified in 4/150 (2.6%), 8/993 (0.8%), and 0/70 of pediatric, adult, and elderly patients, respectively. Eight patients had a WBC count >50 × 10(9) /L. Ten cases had an evaluable immunophenotyping. A B or T precursor ALL occurred in 7 and 3 patients, respectively. Eleven/12 patients (92%) achieved CR. At 48 months, overall survival and event-free survival rates were 73.3% and 67%, respectively. At CR, a parallel RT-PCR evaluation of the MLL/ENL expression was available in 5 cases. Of these latter, 2 tested MLL/ENL-negative and 3 positive. The minimal residual disease molecular monitoring showed that MLL/ENL status did not correlate with outcome. In fact, all the 2 PCR-negative and 1 of the 3 PCR-positive cases relapsed. Further, a MLL/ENL expression, not preceding a relapse, was detected several times during the follow-up of five long-survivors. In conclusion, also in adults, the MLL/ENL fusion identifies a rare leukemic entity with a favorable prognosis. The observed inconsistency between the clinical cure and the presence of detectable MLL/ENL transcript suggests the existence of a MLL/ENL-expressing "preleukemia" stem cells, similar to what demonstrated for the AML1/ETO-positive leukemia setting.