Contributions
Abstract: PB1357
Type: Publication Only
Session title: Acute lymphoblastic leukemia - Biology & Translational Research
Background
Screening at onset for BCR-ABL1 fusion gene by FISH/RT-PCR and chromosome banding analysis is mandatory and routinely tested for a rapid diagnosis in Acute Limphoblastic Leukemia (ALL). Philadelphia chromosome in adult ALL patients was associated with an unfavorable prognosis before the introduction of tyrosin kinase inhibitors. However, a proportion of patients still have an unfavorable prognosis, suggesting that additional biological mechanisms, like additional chromosomal abnormalities (ACAs), other than the BCR-ABL1 driver lesion, are involved. The application of high-resolution genome wide methods is useful for understanding the molecular bases of these mechanisms.
We report the case of a 42 years old male with Ph+ ALL confirmed by RT-PCR (p190BCR-ABL) with a normal karyotype in all the observed metaphases and an abnormal FISH signal pattern (four fusion signals) detected only in nuclei.
Aims
To assess the real nature of an atypical cytogenetically undetectable rearrangement of BCR-ABL1 in a ALL patient we investigated his bone marrow sample with a microarray-based approach.
Methods
DNA obtained from bone marrow of the patient was analyzed by Comparative Genomic Hybridization (CGH) 60K oligonucleotide array. Fluorescence in situ hybridization (FISH) was performed to confirm the result obtained.
Results
CGH array detected a clone (20% of cells) with an additional X chromosome, trisomy of chromosomes 4, 5, 20, and 21 and a 3.8 MB interstitial deletion of short arm of chromosome 9. This region contains several genes including CDKN2A/2B, recently emerged as very strong prognostic marker in Ph+ ALL adult patients. Moreover, our analysis showed a gain of two copies of 9q34-qter and 22pter-q11.2 regions suggesting the presence of two additional Philadelphia chromosomes. This abnormal clone was confined to nuclei, as confirmed by FISH. Karyotype analysis needs the presence of mitotic cells that have been arrested in the metaphase. In this case probably only normal cells were actively dividing. This explains the normal karyotype displayed by the cytogenetic analysis. At the present time the patient, at day 45 from therapy start, is responding to the induction therapy with imatinib and prednisone, with minimal residual disease persistence.
Conclusion
Most of ACAs, frequently observed in Ph+ ALL, are detectable by chromosome analysis. The presence of ACAs in adult Ph+ ALL seems to negatively influence the prognosis and consequently the efficacy of TKI combined with chemotherapy and hematopoietic stem cell transplantation.
When a normal karyotype is detected, screening for recurrent fusion genes and rapid diagnosis for clinically relevant anomalies by FISH or RT-PCR represent the gold standard methods in genetic analysis of ALL. Anyway, these methods may not be able to detect cryptic genetic lesions. It is well known that a normal karyotype can hide a more complex condition. This is due to the low resolution of the cytogenetic analysis and to the different clone proliferation leading to cell selection. This case underlines that to overcome these limitations may be useful to include microarray-based genome wide test in the diagnostic workup that could provide insight into the molecular pathogenesis of Ph+ ALL and help to define more accurately prognostic groups.
In particular, CGH array can easily identify small and very often cytogenetically undetectable CDKN2A/2B deletions that recently emerged as a new strong and independent prognostic marker in Ph+ ALL adult patients.
Keyword(s): CGH, FISH, Ph+ ALL
Abstract: PB1357
Type: Publication Only
Session title: Acute lymphoblastic leukemia - Biology & Translational Research
Background
Screening at onset for BCR-ABL1 fusion gene by FISH/RT-PCR and chromosome banding analysis is mandatory and routinely tested for a rapid diagnosis in Acute Limphoblastic Leukemia (ALL). Philadelphia chromosome in adult ALL patients was associated with an unfavorable prognosis before the introduction of tyrosin kinase inhibitors. However, a proportion of patients still have an unfavorable prognosis, suggesting that additional biological mechanisms, like additional chromosomal abnormalities (ACAs), other than the BCR-ABL1 driver lesion, are involved. The application of high-resolution genome wide methods is useful for understanding the molecular bases of these mechanisms.
We report the case of a 42 years old male with Ph+ ALL confirmed by RT-PCR (p190BCR-ABL) with a normal karyotype in all the observed metaphases and an abnormal FISH signal pattern (four fusion signals) detected only in nuclei.
Aims
To assess the real nature of an atypical cytogenetically undetectable rearrangement of BCR-ABL1 in a ALL patient we investigated his bone marrow sample with a microarray-based approach.
Methods
DNA obtained from bone marrow of the patient was analyzed by Comparative Genomic Hybridization (CGH) 60K oligonucleotide array. Fluorescence in situ hybridization (FISH) was performed to confirm the result obtained.
Results
CGH array detected a clone (20% of cells) with an additional X chromosome, trisomy of chromosomes 4, 5, 20, and 21 and a 3.8 MB interstitial deletion of short arm of chromosome 9. This region contains several genes including CDKN2A/2B, recently emerged as very strong prognostic marker in Ph+ ALL adult patients. Moreover, our analysis showed a gain of two copies of 9q34-qter and 22pter-q11.2 regions suggesting the presence of two additional Philadelphia chromosomes. This abnormal clone was confined to nuclei, as confirmed by FISH. Karyotype analysis needs the presence of mitotic cells that have been arrested in the metaphase. In this case probably only normal cells were actively dividing. This explains the normal karyotype displayed by the cytogenetic analysis. At the present time the patient, at day 45 from therapy start, is responding to the induction therapy with imatinib and prednisone, with minimal residual disease persistence.
Conclusion
Most of ACAs, frequently observed in Ph+ ALL, are detectable by chromosome analysis. The presence of ACAs in adult Ph+ ALL seems to negatively influence the prognosis and consequently the efficacy of TKI combined with chemotherapy and hematopoietic stem cell transplantation.
When a normal karyotype is detected, screening for recurrent fusion genes and rapid diagnosis for clinically relevant anomalies by FISH or RT-PCR represent the gold standard methods in genetic analysis of ALL. Anyway, these methods may not be able to detect cryptic genetic lesions. It is well known that a normal karyotype can hide a more complex condition. This is due to the low resolution of the cytogenetic analysis and to the different clone proliferation leading to cell selection. This case underlines that to overcome these limitations may be useful to include microarray-based genome wide test in the diagnostic workup that could provide insight into the molecular pathogenesis of Ph+ ALL and help to define more accurately prognostic groups.
In particular, CGH array can easily identify small and very often cytogenetically undetectable CDKN2A/2B deletions that recently emerged as a new strong and independent prognostic marker in Ph+ ALL adult patients.
Keyword(s): CGH, FISH, Ph+ ALL