Analysis of ETV6/AML1 abnormalities in acute lymphoblastic leukaemia: incidence, alternative spliced forms and minimal residual disease value

Abstract

Summary. The t(12;21)(p13;q22) translocation, resulting in the fusion of the ETV6 and AML1 genes, occurs in 20±25% of paediatric B-lineage acute lymphoblastic leukaemias (ALL). The identification of the fusion product has important prognostic and therapeutic implications as the translocation has been associated with a favourable clinical outcome. The aim of this study was threefold: (i) to assess the frequency and clinical association of the fusion gene in patients with and without a cytogenetically detectable chromosome 12 and/or 21 abnormality or failed cytogenetic results, (ii) to characterize alternative forms of ETV6/AML1 transcripts, and (iii) to use ETV6/AML1 as a molecular marker for the investigation of minimal residual disease (MRD). ETV6/AML1 fusion was detected in 22 (39%) of 56 cases studied by reverse transcriptase polymerase chain reaction (RT-PCR). ETV6/AML1 fusion was found in nine out of 16 (56%) cases with a cytogenetically visible chromosome 12 abnormality, but also in nine out of 29 patients (31%) without a chromosome 12 abnormality or patients with failed cytogenetics (four out of 11 patients, 36%), making this the most common cytogenetic abnormality in childhood ALL. Alternatively spliced ETV6/AML1 forms were investigated in 14 of the positive patients. Exon 5 of ETV6 was fused in frame to all AML1 exons, except exon 4. Fusion to exon 6 of AML1 resulted in one amino acid change. The presence of ETV6/AML1 was associated with a lower white blood cell count (Student's t-test; P 0´009) and common (c)ALL phenotype (x 2 test; P . 0´001), but no better disease-free survival. Our study shows that (i) RT-PCR is the most effective approach for the detection of t(12;21) in childhood ALL, (ii) the association of ETV6/AML1 and chromosome 12 and/or 21, seen in 56% of our cases, further confirms existing data, (iii) overall survival of patients with t(12;21) was not better than other cytogenetics groups, and (d) MRD analysis using ETV6/AML1 fusion is specific, but not sensitive enough to avoid false negative results.Keywords: ETV6 gene, 12p abnormality, leukaemia, ETV6/ AMLI.The translocation t(12;21)(p13;q22) is the most common chromosomal abnormality in childhood acute lymphoblastic leukaemia (ALL) occurring in 25% of cases (Golub et al, 1994; Romana et al, 1995a, b;Shurtleff et al, 1995;Borkhardt et al, 1997;Cave et al, 1997;Raimondi et al, 1997). The translocation involves the ETV6 gene at 12p13 and the AML1 gene at 21q22. As it is invisible using conventional cytogenetics, fluorescence in situ hybridization (FISH) and reverse transcriptase polymerase chain reaction (RT-PCR) amplification of the fusion mRNA are now the methods of choice for its detection. The ETV6 gene, a member of the E26 transformation-specific (ETS) family of transcription factors Wlodarska et al, 1996Wlodarska et al, , 1998, was first characterized by its involvement in the t(5;12)(q33;p13) translocation in a case of chronic myelomonocytic leukaemia (Golub et al, 1994;Todd et al, 1995). The gene consists of eight exons, of which ...

Outcome of ETV6/RUNX1‐positive childhood acute lymphoblastic leukaemia in the NOPHO‐ALL‐1992 protocol: frequent late relapses but good overall survival

“…A relatively high frequency of late relapses, i.e., off therapy, has been emphasized by several groups (Nakao et al , 1996; Harbott et al , 1997; Seeger et al , 1998, 1999; Takahashi et al , 1998; Avigad et al , 1999; Codrington et al , 2000; Tsang et al , 2001). In the present series, almost 50% of all relapses after 5 years and 80% of those after 6 years occurred in t(12;21)‐positive patients.…”

“…Most studies on the prognostic implications of t(12;21) have not reported individual data on gender and time in remission. However, the information that can be retrieved from studies providing pertinent data (Nakao et al , 1996; Harbott et al , 1997; Lanza et al , 1997; Satake et al , 1997; Loh et al , 1998; Rubnitz et al , 1999; Codrington et al , 2000; de Haas et al , 2000; Seeger et al , 2001; Tsang et al , 2001; Alvarez et al , 2005; Al‐Sweedan et al , 2007) does not support that boys generally relapse later than girls; based on all studies referred to above, the median remission duration before relapse was 37 months (range 17–102) for boys and 32 months (range 11–109) for girls. Thus, our finding may well be fortuitous and should be interpreted with caution.…”

“…Similar data indicating a favourable outcome for this patient cohort have since come from several retrospective studies (McLean et al , 1996; Borkhardt et al , 1997; Avigad et al , 1999; Maloney et al , 1999; Jamil et al , 2000; Uckun et al , 2001) as well as from a recent prospective study in which the survival rate was significantly better for BCP ALLs with ETV6/RUNX1 than for those without this fusion (Loh et al , 2006). However, many investigators have not observed any statistically significant survival differences between t(12;21)‐positive and ‐negative ALLs (Lanza et al , 1997; Takahashi et al , 1998; Kempski et al , 1999; Codrington et al , 2000; Hann et al , 2001; Hubeek et al , 2001; Pajor et al , 2001). Furthermore, frequent late relapses and similar incidences of the ETV6/RUNX1 transcript in ALLs at diagnosis and relapse have been noted by some (Nakao et al , 1996; Harbott et al , 1997; Seeger et al , 1998, 1999; Tsang et al , 2001) but not by other authors (Loh et al , 1998; Rubnitz et al , 1999; Zuna et al , 1999).…”