T-cell acute lymphoblastic leukemias (T-ALL) are immature lymphoid tumors localizing in the bone marrow, mediastinum, central nervous system, and lymphoid organs. They account for 10–15% of pediatric and about 25% of adult acute lymphoblastic leukemia (ALL) cases. It is a widely heterogeneous disease that is caused by the co-occurrence of multiple genetic abnormalities, which are acquired over time, and once accumulated, lead to full-blown leukemia. Recurrently affected genes deregulate pivotal cell processes, such as cycling (CDKN1B, RB1, TP53), signaling transduction (RAS pathway, IL7R/JAK/STAT, PI3K/AKT), epigenetics (PRC2 members, PHF6), and protein translation (RPL10, CNOT3). A remarkable role is played by NOTCH1 and CDKN2A, as they are altered in more than half of the cases. The activation of the NOTCH1 signaling affects thymocyte specification and development, while CDKN2A haploinsufficiency/inactivation, promotes cell cycle progression. Among recurrently involved oncogenes, a major role is exerted by T-cell-specific transcription factors, whose deregulated expression interferes with normal thymocyte development and causes a stage-specific differentiation arrest. Hence, TAL and/or LMO deregulation is typical of T-ALL with a mature phenotype (sCD3 positive) that of TLX1, NKX2-1, or TLX3, of cortical T-ALL (CD1a positive); HOXA and MEF2C are instead over-expressed in subsets of Early T-cell Precursor (ETP; immature phenotype) and early T-ALL. Among immature T-ALL, genomic alterations, that cause BCL11B transcriptional deregulation, identify a specific genetic subgroup. Although comprehensive cytogenetic and molecular studies have shed light on the genetic background of T-ALL, biomarkers are not currently adopted in the diagnostic workup of T-ALL, and only a limited number of studies have assessed their clinical implications. In this review, we will focus on recurrent T-ALL abnormalities that define specific leukemogenic pathways and on oncogenes/oncosuppressors that can serve as diagnostic biomarkers. Moreover, we will discuss how the complex genomic profile of T-ALL can be used to address and test innovative/targeted therapeutic options.

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Acute leukemias (AL) of ambiguous lineage are a heterogeneous group of high-risk leukemias characterized by co-expression of myeloid and lymphoid markers. In this study, we identified a distinct subgroup of immature acute leukemias characterized by a broadly variable phenotype, covering acute myeloid leukemia (AML M0 or M1), T/myeloid mixed phenotype acute leukemia (T/M MPAL), and early T-cell precursor acute lymphoblastic leukemia (ETP-ALL). Rearrangements at 14q32/BCL11B are the cytogenetic hallmark of this entity. In our screening of 915 hematological malignancies, there were 202 AML and 333 T-cell Acute Lymphoblastic Leukemia (T-ALL) (58 ETP, 178 non-ETP, 8 T/M MPAL, 89 not otherwise specified). We identified 20 cases of immature leukemias (4% of AML and 3,6% of T-ALL) harbouring four types of 14q32/BCL11B translocations: t(2,14)(q22.3;q32) (n=7), t(6;14)(q25.3;q32) (n=9), t(7;14)(q21.2;q32) (n=2) and t(8;14)(q24.2;q32) (n=2). The t(2;14) produced a ZEB2-BCL11B fusion transcript, while the other three rearrangements displaced transcriptionally active enhancer sequences close to BCL11B without producing fusion genes. All translocations resulted in the activation of BCL11B, a regulator of T-cell differentiation associated with transcriptional corepressor complexes in mammalian cells. The expression of BCL11B behaved as a disease biomarker, which was present at diagnosis but not in remission. Deregulation of BCL11B co-occurred with variants at FLT3 and at epigenetic modulators, most frequently DNMT3A, TET2 and/or WT1 gene. Transcriptome analysis identified a specific expression signature, with significant downregulation of BCL11B targets, and clearly separating BCL11B positive AL from AML, T-ALL, and ETP-ALL. Remarkably, ex-vivo drug sensitivity profile identified a panel of compounds with effective antileukemic activity.

We investigated MYB rearrangements (MYB‐R) and the levels of MYB expression, in 331 pediatric and adult patients with T‐cell acute lymphoblastic leukemia (T‐ALL). MYB‐R were detected in 17 cases and consisted of MYB tandem duplication (tdup) (= 14) or T cell receptor beta locus (TRB)‐MYB (= 3). As previously reported, TRB‐MYB was found only in children (1.6%) while MYB tdup occurred in both age groups, although it was slightly more frequent in children (5.2% vs 2.8%). Shared features of MYB‐R T‐ALL were a non‐early T‐cell precursor (ETP) phenotype, a high incidence of NOTCH1/FBXW7 mutations (81%) and CDKN2AB deletions (70.5%). Moreover, they mainly belonged to HOXA (=8), NKX2‐1/2‐2/TLX1 (=4), and TLX3 (=3) homeobox‐related subgroups. Overall, MYB‐R cases had significantly higher levels of MYB expression than MYB wild type (MYB‐wt) cases, although high levels of MYB were detected in ~ 30% of MYB‐wt T‐ALL. Consistent with the transcriptional regulatory networks, cases with high MYB expression were significantly enriched within the TAL/LMO subgroup (P = .017). Interestingly, analysis of paired diagnosis/remission samples demonstrated that a high MYB expression was restricted to the leukemic clone. Our study has indicated that different mechanisms underlie MYB deregulation in 30%‐40% of T‐ALL and highlighted that, MYB has potential as predictive/prognostic marker and/or target for tailored therapy.

The catalytic activity of human Telomerase Reverse Transcriptase (TERT) compensates for the loss of telomere length, eroded during each cell cycle, to ensure a correct division of stem and germinal cells. In human tumors, ectopic TERT reactivation, most frequently due to hotspot mutations in the promoter region (TERTp), i.e. c.1-124 C > T, c.1-146 C > T, confers a proliferative advantage to neoplastic cells. In gliomas, TERTp mutations (TERTp mut) mainly occur in oligodendroglioma and glioblastoma. We screened, for TERTp hotspot mutations, 301 adult patients with gliomas and identified heterozygous mutations in 239 cases: 94% of oligodendroglioma, 85% of glioblastoma, and 37.5% of diffuse/anaplastic astrocytoma. Besides the recurrent c.1-124 C > T and c.1-146 C > T, two cases of glioblastoma harbored novel somatic TERTp variants, which consisted of a tandem duplications of 22 nucleotides, i.e. a TERTp c.1-100_1-79dup and TERTp c.1-110_1-89, both located downstream c.1-124 C > T and c.1-146 C > T. In silico analysis predicted the formation of 119 and 108 new transcription factor's recognition sites for TERTp c.1-100_1-79dup and TERTp c.1-110_1-89, respectively. TERTp duplications (TERTp dup) mainly affected the binding capacity of two transcription factors' families, i.e. the members of the E-twenty-six and the Specificity Protein/Krüppel-Like Factor groups. In fact, these new TERTpdup significantly enhanced the E-twenty-six transcription factors' binding capacity, which is also typically increased by the two c.1-124 C > T/c.1-146 C > T hotspot TERTp mut. On the other hand, they were distinguished by enhanced affinity for the Krüppel proteins. The luciferase assay confirmed that TERTp dup behaved as gain-of-function mutations causing a 2,3-2,5 fold increase of TERT transcription. The present study provides new insights into TERTp mutational spectrum occurring in central nervous system tumors, with the identification of new recurrent somatic gain-of-function mutations, occurring in 0.8% of glioblastoma IDH-wildtype.