Minimal residual disease-based treatment is adequate for relapse-prone childhood acute lymphoblastic leukemia with an intrachromosomal amplification of chromosome 21: the experience of the ALL-BFM 2000 trial.

BACKGROUND: Recently, the UK CCLG and COG reported that an intrachromosomal amplification of chromosome 21 (iAMP21) in acute lymphoblastic leukemia (ALL) loses its adverse prognostic impact with intensified therapy. PATIENT AND METHODS: We evaluated the prognosis of iAMP21 among patients from the ALL-BFM (Berlin-Frankfurt-Münster) 2000 trial with 46 of 2 637 (2%) patients iAMP21+. RESULTS: 8-year event-free-survival (EFS, 64 ± 8% vs. 81 ± 1%, p=0.0026) and cumulative incidence of relapse (CIR, 29 ± 8% vs. 14 ± 1%, p=0.008) of the iAMP21 cases were significantly worse compared with non-iAMP21 patients. Within the MRD low-risk group, iAMP21 cases (n=14) had an inferior 8-year EFS (76 ± 12% vs. 92 ± 1%, p=0.0081), but no increased CIR (10 ± 10% vs. 6 ± 1%, p=0.624). Within the MRD intermediate-risk group, iAMP21 cases (n=27) had a worse 8-year EFS (56 ± 11% vs. 78 ± 2%, p=0.0077) and CIR (44 ± 11% vs. 20 ± 2%, p=0.003) with 6/10 relapses occurring after 2 years. CONCLUSIONS: Conclusively, we believe that there is no necessity for enrolling all iAMP21 patients into the high-risk arm of ongoing ALL-BFM trials because MRD low-risk patients have a moderate relapse risk under current therapy. Whether the increased relapse risk in MRD intermediate-risk patients can be avoided by late treatment intensification remains to be answered by the AIEOP-BFM ALL 2009 trial randomly using protracted pegylated L-asparaginase during delayed intensification and early maintenance.

Sporadic hypercalcitoninemia: clinical and therapeutic consequences.

'Calcitonin screening' is not accepted as the standard of care in daily practice. The clinical and surgical consequences of 'calcitonin screening' in a series of patients with mildly elevated basal calcitonin and pentagastrin stimulated calcitonin levels are presented. 260 patients with elevated basal (>10 pg/ml) and stimulated calcitonin levels (>100 pg/ml) were enrolled in this prospective study. None of the patients was member of a known medullary thyroid carcinoma family. Thyroidectomy and bilateral central and lateral neck dissections were performed. Testing for the presence of germ-line mutations was performed in all patients. Histological and immunohistochemical findings were compared with basal and stimulated calcitonin levels. All patients were subsequently followed biochemically. C-cell hyperplasia (CCH) was found in 126 (49%) and medullary thyroid cancer was found in 134 (51%) patients. RET proto-oncogen mutations were documented in 22 (8%) patients (medullary thyroid cancer:18, CCH:4). In 56 (46%) of 122 patients, sporadic CCH was classified neoplastic ('carcinoma in situ'). Of 97 (72%; 10 with hereditary medullary thyroid cancer) had pT1 (International Union against Cancer recommendations 2002) and 33 (25%) had pT2 or pT3 and 4 (3%) pT4 tumors. Of 39 (29.1%) had lymph node metastases. 106 (79.1%; 15 (38.5%) with lymph node metastases) patients were cured. Evaluation of basal and stimulated calcitonin levels enables the prediction of medullary thyroid cancer. All patients with basal calcitonin >64 pg/ml and stimulated calcitonin >560 pg/ml have medullary thyroid cancer. Medullary thyroid cancer was documented in 20% of patients with basal calcitonin >10 pg/ml but <64 pg/ml and stimulated calcitonin >100 pg/ml but <560 pg/ml.

Evaluation of antileukaemic effects of rapamycin in patients with imatinib-resistant chronic myeloid leukaemia.

BACKGROUND: Recent data suggest that the mammalian target of rapamycin (mTOR) is involved in the regulation of growth of neoplastic cells in chronic myeloid leukaemia (CML). PATIENTS AND METHODS: We treated six patients with imatinib-resistant CML in haematological relapse (leukocytes > 20,000 microL(-1)) with rapamycin at 2 mg per os daily for 14 consecutive days, with dose-adjustment allowed to reach a target rapamycin serum concentration of 10-20 pg mL(-1). RESULTS: A major leukocyte response with decrease to less than 10,000 microL(-1) was obtained in two patients, and a minor transient response was seen in two other patients. In responding patients, we also observed a decrease in vascular endothelial growth factor (VEGF) mRNA levels in circulating leukaemic cells. Side effects during rapamycin treatment were mild in most patients. In one patient, pneumonia developed. Rapamycin was also found to counteract growth of CML cells in vitro as determined by (3)H-thymidine incorporation. Moreover, rapamycin inhibited the growth of Ba/F3 cells exhibiting various imatinib-resistant mutants of BCR/ABL, including the T315I variant that exhibits resistance against most currently available BCR/ABL kinase inhibitors. CONCLUSIONS: Rapamycin shows antileukaemic effects in imatinib-resistant CML in vitro and in vivo. Larger trials with rapamycin or rapamycin-derivatives in combination with other targeted drugs are warranted to further determine clinical efficacy in CML.

Comorbidity predicts survival in myelodysplastic syndromes or secondary acute myeloid leukaemia after allogeneic stem cell transplantation.

BACKGROUND: Recent data suggest that, among other factors, comorbidity may be an important prognostic variable in patients with myelodysplastic syndromes (MDS) who are eligible for haematopoietic stem cell transplantation (SCT). PATIENTS AND METHODS: We examined the overall survival (OS) and underlying risk factors in 45 adult patients with MDS (n = 38), chronic myelomonocytic leukaemia (n = 1), or secondary acute myeloid leukaemia (AML) arising from MDS (n = 6), who underwent allogeneic SCT at our Institution. RESULTS: With a median follow-up of 37 months, OS for all patients was 23%, post-transplant relapse occurred in 11 patients, and 10 patients died from treatment-related complications. The overall outcome and survival was independent of cytogenetic abnormalities and International Prognostic Scoring System (IPSS). However, we identified comorbidity as defined by the haematopoietic cell transplantation specific comorbidity index (HCT-CI), as a significant adverse prognostic variable in our MDS patients. CONCLUSIONS: Based on these data and similar published data we recommend selecting patients with MDS or secondary AML for SCT according to the presence of comorbidities.

Clinical and prognostic significance of histamine monitoring in patients with CML during treatment with imatinib (STI571).

BACKGROUND: Although imatinib is highly effective in chronic myeloid leukemia (CML), drug-resistance may occur. Therefore, monitoring of minimal residual disease (MRD) during treatment with imatinib is important. However, most MRD-parameters are expensive and require special technology. We determined the value of histamine as MRD-marker in CML. PATIENTS AND METHODS: Histamine levels were measured serially in whole blood samples before and during imatinib therapy in 80 CML patients by radioimmunoassay. RESULTS: Histamine levels were highly upregulated in CML at diagnosis compared to healthy controls, and correlated with the presence of basophils. During treatment with imatinib, histamine levels decreased and returned to normal levels in those achieving a complete cytogenetic response (CCR). Loss of CCR during therapy was invariably accompanied by an increase in histamine. Moreover, a histamine level of >100 ng/ml three or six months after start of imatinib was associated with a significantly reduced probability of survival (p<0.05). Whereas basophils were found to correlate well with histamine during imatinib, no correlations were found between histamine and Ph+ metaphases or histamine and BCR/ABL. CONCLUSION: Histamine-monitoring during treatment with imatinib is of prognostic significance.

The MLL recombinome of acute leukemias.

Chromosomal rearrangements of the human MLL gene are a hallmark for aggressive (high-risk) pediatric, adult and therapy-associated acute leukemias. These patients need to be identified in order to subject these patients to appropriate therapy regimen. A recently developed long-distance inverse PCR method was applied to genomic DNA isolated from individual acute leukemia patients in order to identify chromosomal rearrangements of the human MLL gene. We present data of the molecular characterization of 414 samples obtained from 272 pediatric and 142 adult leukemia patients. The precise localization of genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) was determined and several new TPGs were identified. The combined data of our study and published data revealed a total of 87 different MLL rearrangements of which 51 TPGs are now characterized at the molecular level. Interestingly, the four most frequently found TPGs (AF4, AF9, ENL and AF10) encode nuclear proteins that are part of a protein network involved in histone H3K79 methylation. Thus, translocations of the MLL gene, by itself coding for a histone H3K4 methyltransferase, are presumably not randomly chosen, rather functionally selected.

Genomic and transcriptional landscape of P2RY8-CRLF2-positive childhood acute lymphoblastic leukemia.

Children with P2RY8-CRLF2-positive acute lymphoblastic leukemia have an increased relapse risk. Their mutational and transcriptional landscape, as well as the respective patterns at relapse remain largely elusive. We, therefore, performed an integrated analysis of whole-exome and RNA sequencing in 41 major clone fusion-positive cases including 19 matched diagnosis/relapse pairs. We detected a variety of frequently subclonal and highly instable JAK/STAT but also RTK/Ras pathway-activating mutations in 76% of cases at diagnosis and virtually all relapses. Unlike P2RY8-CRLF2 that was lost in 32% of relapses, all other genomic alterations affecting lymphoid development (58%) and cell cycle (39%) remained stable. Only IKZF1 alterations predominated in relapsing cases (P=0.001) and increased from initially 36 to 58% in matched cases. IKZF1's critical role is further corroborated by its specific transcriptional signature comprising stem cell features with signs of impaired lymphoid differentiation, enhanced focal adhesion, activated hypoxia pathway, deregulated cell cycle and increased drug resistance. Our findings support the notion that P2RY8-CRLF2 is dispensable for relapse development and instead highlight the prominent rank of IKZF1 for relapse development by mediating self-renewal and homing to the bone marrow niche. Consequently, reverting aberrant IKAROS signaling or its disparate programs emerges as an attractive potential treatment option in these leukemias.

Genotype-outcome correlations in pediatric AML: the impact of a monosomal karyotype in trial AML-BFM 2004.

We conducted a cytogenetic analysis of 642 children with de novo acute myeloid leukemia (AML) treated on the AML-Berlin-Frankfurt-Münster (BFM) 04 protocol to determine the prognostic value of specific chromosomal aberrations including monosomal (MK+), complex (CK+) and hypodiploid (HK+) karyotypes, individually and in combination. Multivariate regression analysis identified in particular MK+ (n=22) as a new independent risk factor for poor event-free survival (EFS 23±9% vs 53±2% for all other patients, P=0.0003), even after exclusion of four patients with monosomy 7 (EFS 28±11%, P=0.0081). CK+ patients without MK had a better prognosis (n=47, EFS 47±8%, P=0.46) than those with MK+ (n=12, EFS 25±13%, P=0.024). HK+ (n=37, EFS 44±8% for total cohort, P=0.3) influenced outcome only when t(8;21) patients were excluded (remaining n=16, EFS 9±8%, P<0.0001). An extremely poor outcome was observed for MK+/HK+ patients (n=10, EFS 10±10%, P<0.0001). Finally, isolated trisomy 8 was also associated with low EFS (n=16, EFS 25±11%, P=0.0091). In conclusion, monosomal karyotype is a strong and independent predictor for high-risk pediatric AML. In addition, isolated trisomy 8 and hypodiploidy without t(8;21) coincide with dismal outcome. These results have important implications for risk stratification and should be further validated in independent pediatric cohorts.

Small supernumerary marker chromosomes--progress towards a genotype-phenotype correlation.

Small supernumerary marker chromosomes (sSMC) are still a major problem in clinical cytogenetics as they are too small to be characterized for their chromosomal origin by traditional banding techniques, but require molecular cytogenetic techniques for their identification. Apart from the correlation of about one third of the sSMC cases with a specific clinical picture, i.e. the i(18p), der(22), i(12p) (Pallister Killian syndrome) and inv dup(22) (cat-eye) syndromes, most of the remaining sSMC have not yet been correlated with clinical syndromes. Recently, we reviewed the available >1600 sSMC cases (Liehr T, sSMC homepage: http://mti-n.mti.uni-jena.de/~huwww/MOL_ZYTO/sSMC.htm). A total of 387 cases (including the 45 new cases reported here) have been molecularly cytogenetically characterized with regard to their chromosomal origin, the presence of euchromatin, heterochromatin and satellite material. Based on analysis of these cases we present the first draft of a basic genotype-phenotype correlation for sSMC for all human chromosomes apart from the chromosomes Y, 10, 11 and 13.

MDR1 gene expression and treatment outcome in acute myeloid leukemia.

To prospectively assess the role of MDR1 gene expression in patients with de novo acute myeloid leukemia (AML), levels of MDR1 RNA in blast cells were determined at diagnosis and correlated with treatment outcome in 63 patients. MDR1 RNA levels were negative in 29% and positive in 71% of the patients. The complete remission rate in response to induction chemotherapy was 89% for MDR1 RNA-negative patients and 53% for MDR1 RNA-positive patients (P = .008). Expression of the MDR1 gene was observed in most patients who died early or had resistant disease. Kaplan-Meier curves revealed a decrease in both disease-free survival and overall survival of patients with detectable MDR1 gene expression compared with the disease-free survival and overall survival of MDR1 RNA-negative patients (P = .029 and P = .009, respectively). These data indicate that MDR1 gene expression is an unfavorable prognostic factor and suggest that multidrug resistance is important in AML.

Cloning and characterization of AFX, the gene that fuses to MLL in acute leukemias with a t(X;11)(q13;q23).

We report the cloning and characterization of the entire AFX gene which fuses to MLL in acute leukemias with a t(X;ll)(q13;q23). AFX consists of two exons and encodes for a protein of 501 amino acids. We found that normal B- and T-cells contain similar levels of AFX mRNA and that both the MLL/AFX as well as the AFX/MLL fusion transcripts are present in the cell line and the ANLL sample with a t(X;11)(q13;q23). The single intron of the AFX gene consists of 3706 nucleotides. It contains five simple sequence repeats with lengths of at least 12 bps, a chi-like octamer sequence (GCA/TGGA/TGG) and several immunoglobulin heptamer-like sequences (GATAGTG) that are distributed throughout the entire AFX intron sequence. In the KARPAS 45 cell line the breakpoints occur at nucleotides 2913/2914 of the AFX intron and at nucleotides 4900/4901 of the breakpoint cluster region of the MLL gene. The AFX protein belongs to the forkhead protein family. It is highly homologous to the human FKHR protein, the gene of which is disrupted by the t(2;13)(q35;q14), a chromosome rearrangement characteristic of alveolar rhabdomyosarcomas. It is noteworthy that the t(X;11)(q13;q23) in the KARPAS 45 cell line and in one acute nonlymphoblastic leukemia (ANLL) disrupts the forkhead domain of the AFX protein exactly at the same amino acids as does the t(2;13)(q35;q14) in case of the FKHR protein. In addition, the 5'-part of the AFX protein contains a conserved hexapeptide motif (QIYEWM) that is homologous to the functionally important conserved hexapeptide QIYPWM upstream of the homeobox domain in Hox proteins. This motif mediates the co-operative DNA binding of Pbx family members and Hox proteins and, therefore, plays an important role in physiologic and oncogenic processes. In acute leukemias with a t(X;11)(q13;q23), this hexapeptide motif is separated from the remaining forkhead domain within the AFX protein. The predicted amino acid sequence of AFX differs significantly from the partial AFX protein sequence published previously (Genes, Chromosomes and Cancer, 1994, 11, 79-84). This discrepancy can be explained by the occurrence of two sequencing errors in the earlier work at nucleotide number 783 and 844 (loss of a cytosine residue or guanosine residue, respectively) that lead to two reading frame shifts.

Biased distribution of chromosomal breakpoints involving the MLL gene in infants versus children and adults with t(4;11) ALL.

Derivative chromosomes of 40 patients diagnosed with t(4;11) acute lymphoblastic leukemia (ALL) were analysed on the genomic DNA level. Chromosomal breakpoints were identified in most cases within the known breakpoint cluster regions of the involved MLL and AF4 genes. Due to our current knowledge of the primary DNA sequences of both breakpoint cluster regions, specific features were identified at the chromosomal fusion sites, including deletions, inversions and duplications of parental DNA sequences. After separation of all t(4;11) leukemia patients into two age classes (below and above 1 year of age), the analysis of chromosomal fusion sites revealed significant differences in the distribution of chromosomal breakpoints and led to the definition of two hotspot areas within the MLL breakpoint cluster region. This may point to the possibility of different age-linked mechanisms that were leading to t(4;11) chromosomal translocations.

Competitive CBFbeta/MYH11 reverse-transcriptase polymerase chain reaction for quantitative assessment of minimal residual disease during postremission therapy in acute myeloid leukemia with inversion(16): a pilot study.

PURPOSE: (1) Quantification of minimal residual disease (MRD) by competitive CBFbeta/MYH11 reverse-transcriptase polymerase chain reaction (RT-PCR) in patients with acute myeloid leukemia (AML) and inversion(16) [inv(16)] during postremission therapy, (2) comparison of this method with conventional two-step RT-PCR, and (3) evaluation of a potential prognostic value. PATIENTS AND METHODS: MRD of six consecutive adult patients with AML and inv(16)(p13;q22) or t(16;16)(p13;q22) who entered complete remission (CR) was monitored by competitive CBFbeta/MYH11 RT-PCR in their bone marrow (BM) during postremission therapy with high-dose cytarabine (HiDAC) or after BM transplantation with a matched unrelated-donor marrow (MUD-BMT) during an observation period of 4.5 to 27 months after initiation of treatment. RESULTS: Competitive PCR showed a gradual decline by at least 4 orders of magnitude after 7 to 9 months in patients in continuous CR (CCR), while one patient who relapsed after 13.5 months only achieved a reduction by 2 orders of magnitude at the end of consolidation therapy. A rapid decrease below the detection limit was observed within 1 month in two patients after MUD-BMT. A temporary reappearance of molecular MRD was observed in these patients during immunosuppression for graft-versus-host disease (GvHD). After reduction of immunosuppression, the level of MRD dropped again below the PCR detection limit. Molecular monitoring by conventional two-step RT-PCR yielded comparable results only when multiple assays per time point were performed, while single-assay RT-PCR gave misleading results. CONCLUSION: Competitive RT-PCR is a valuable tool for molecular monitoring during postremission chemotherapy, as well as after BMT.

Are ABL and BCR imprinted? No definitive answers, but more questions.

The apparent nonrandom contribution of the paternally-derived chromosome 9 and the maternally-derived chromosome 22 to the leukemia-specific translocation t(9;22)(q34;q11) obtained by cytogenetic analysis suggested that the two genes affected by this rearrangement, namely ABL and BCR, are imprinted. The results of recent molecular genetic studies have challenged this notion, since it was shown that both the paternal as well as the maternal BCR- and ABL-alleles may be affected by the translocation event and that both genes may be expressed from both alleles. This paper offers possible explanations for the apparent contradictory results obtained through cytogenetic and molecular genetic means. Based on the few available data concerning their allelic methylation pattern, replication behavior and expression status, as well as by referring to similar problems encountered in other genes whose imprinting status had also remained elusive for a long time, I argue that it still remains likely that ABL and BCR are imprinted.

Non-radioactive detection of the rearranged BCR/ABL sequences amplified by polymerase chain reaction.

The polymerase chain reaction (PCR) is a powerful technique for the detection of the bcr/abl rearrangement in chronic myelogenous leukemia (CML). It allows the exponential amplification of the rearranged region, thus facilitating its detection. The specificity of the bcr/abl cDNA sequence amplified by PCR is most commonly verified by hybridization to a 32P-labeled probe. In this paper, an assay for the colorimetric detection of the amplified bcr/abl fragment is described, which offers several advantages over the use of radioactive probes. We adapted the PCR for synthesis and simultaneous labeling of DNA fragments with a non-radioactive steroid compound called digoxigenin. This labeling procedure was used to generate a digoxigenin-labeled internal probe for the chimeric bcr/abl mRNA. The assay described is based on the hybridization of the amplified bcr/abl sequence to the non-radioactively labeled probe and on the subsequent detection by an enzyme-linked immunoassay and enzyme-catalyzed color reaction. Using this protocol, we investigated 20 patients with CML along with six healthy individuals and two cell lines derived from patients with CML for the presence of the bcr/abl rearrangement. It is shown that the assay is both highly sensitive and specific and that it is readily applicable to the routine diagnosis of CML. In addition, the assay could be adapted to a number of clinical diagnostic uses.

Trisomy 4: a specific karyotype anomaly in primary and secondary acute myeloid leukemia.

Trisomy 4 as single karyotype anomaly has recently been proposed as an acute myeloid leukemia (AML) specific aberration. Up to now, 20 cases have been reported in which the single abnormality occurred without additional chromosomal aberrations. Trisomy 4 has been found in both primary and secondary AML, the majority of cases being diagnosed as FAB M4 or M2 subtypes. In the cytogenetic analysis of 305 patients with AML, we found 209 cases with aberrant karyotypes, among them two patients (22a, male, M2; and 69a, male, M4) with trisomy 4 as single aberration. The younger patient achieved complete remission lasting 13 months and survived 22 months whereas the older patient died in aplastic phase due to septicaemia 5 weeks after admission. Trisomy 4 is proposed to be the primary aberration in both these cases of de novo AML. Although in one case, as in two cases reported earlier, cytogenetic results were only available in first relapse, we have no indication that trisomy 4 appeared in a secondary induced leukemia, because the leukemic blasts of the relapse were morphologically identical to first acute phase. In contrast to other specific chromosomal aberrations, results indicate that trisomy 4 has as yet no prognostic relevance concerning the clinical outcome.

PAX5/ETV6 fusion defines cytogenetic entity dic(9;12)(p13;p13).

Recurrent chromosomal abnormalities present in malignant cells often define subentities with unique biological and clinical features. The molecular identification of genes involved in genetic alterations has led to the characterization of fusion genes with neoplastic properties. However, for many nonrandom translocations including the dic(9;12)(p11-13;p11-12), the molecular equivalent has not as yet been identified. The dicentric translocation dic(9;12) is a recurrent chromosome abnormality that accounts for close to 1% of childhood acute lymphoblastic leukemia (ALL). This specific alteration occurs almost exclusively in B-progenitor ALL, and unlike many other nonrandom translocations, is associated with an excellent prognosis. In this work, we provide strong evidence that the PAX5/ETV6 fusion transcript defines the clinical and biological entity that is associated with the presence of a dic(9;12) chromosome. As the PAX5 and ETV6 genes are localized at 9p13 and 12p13, respectively, the cytogenetic description of the dic(9;12)-PAX5/ETV6 rearrangement should be refined to dic(9;12)(p13;p13).

Use of quantitative polymerase chain reaction to monitor residual disease in chronic myelogenous leukemia during treatment with interferon.

Interferon-alpha (IFN-alpha) has become a widely used treatment modality in chronic myelogenous leukemia (CML) and was shown to induce complete hematologic responses in about 70% of the patients. In a minority of cases, complete suppression of the Philadelphia (Ph)-positive clone has been observed by cytogenetic investigation or by Southern blot analysis. In most instances, however, analyses by the highly sensitive two-step polymerase chain reaction (PCR) reveal the presence of residual leukemic cells despite continuous treatment. Since PCR positivity has not been associated with an increased risk of disease recurrence, the monitoring of cells carrying the characteristic BCR/ABL rearrangement by qualitative PCR may not facilitate early identification of patients who are likely to relapse. We have therefore employed a quantitative PCR technique to monitor the BCR/ABL mRNA expression levels during the course of treatment in an attempt to assess the response to IFN-alpha at the molecular level and to provide a basis for early detection of progressive disease. Twenty CML patients who received therapy with IFN-alpha in first chronic phase of the disease were enrolled in the study. In addition, we have monitored two CML patients treated with IFN-alpha for relapse after bone marrow transplantation. Thirteen patients who displayed decreasing, constant or fluctuating levels of BCR/ABL expression during an observation period of up to 4 years (mean 25 months) have remained in hematologic remission. Two patients showed an elevation in the marker gene expression upon discontinuation of treatment, but no further increase in BCR/ABL mRNA has been observed after reinitiation of therapy with IFN, and the patients have remained in hematologic remission. In seven patients, quantitative PCR (Q-PCR) analyses revealed increasing expression of the chimeric gene during treatment with IFN-alpha. In all seven cases, the detection of elevated BCR/ABL transcripts by quantitative PCR preceded signs of hematologic or cytogenetic disease progression by up to 8 months (median 6 months). Our data show that quantitative PCR analysis facilitates the monitoring of the response to IFN-alpha therapy and provides an effective diagnostic tool for the timely detection of recurrent disease. The employment of this technique greatly enhances the diagnostic possibilities in the management of chronic myelogenous leukemia.

Expression of identical E2A/PBX1 fusion transcripts occurs in both pre-B and early pre-B immunological subtypes of childhood acute lymphoblastic leukemia.

The translocation t(1;19)(q23;p13) in pediatric patients with acute lymphoblastic leukemia (ALL) was demonstrated in early reports to result in a consistent fusion between the E2A and PBX1 gene sequences and in the expression of a uniform, chimeric E2A/PBX1 mRNA with transforming potential. More recent observations suggested that cytogenetically identical t(1;19) translocations can result in the transcription of different mRNA species and that expression of the E2A/PBX1 message may be restricted to patients with the t(1;19) who display a pre-B phenotype of ALL. To further assess the correlation between the immunologic subtypes of the disease and specific genetic alterations, we have performed cytogenetic and molecular analyses in 221 children with B-lineage ALL. Expression of the chimeric E2A/PBX1 message was detected in 21 patients. Out of 14 patients, in whom cytoplasmic immunoglobulin (cig) analyses were available, no less than four had a cig- B-cell precursor ALL, whereas 10 displayed a cig+ B-ALL immunophenotype. These findings are at variance with a recent report in which expression of the E2A/PBX1 message was linked exclusively to a subset of patients who displayed a cig+ pre-B-cell precursor phenotype of ALL. In seven cases diagnosed before 1986, cig analyses were not available, and consequently E2A/PBX1 expression could not be correlated to a particular immunological subtype of B-cell precursor ALL. Our results have important implications for the detection of residual disease in pediatric patients where expression of the typical E2A/PBX1 mRNA may occur both in cig+ (pre-B) and cig- (early pre-B) immunologic subtypes of ALL.