HAEM5:Acute myeloid leukaemia with BCR::ABL1 fusion: Difference between revisions
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{{DISPLAYTITLE:Acute myeloid leukaemia with BCR::ABL1 fusion}} | {{DISPLAYTITLE:Acute myeloid leukaemia with BCR::ABL1 fusion}} | ||
[[HAEM5:Table_of_Contents|Haematolymphoid Tumours ( | [[HAEM5:Table_of_Contents|Haematolymphoid Tumours (5th ed.)]] | ||
{{Under Construction}} | {{Under Construction}} | ||
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}}</blockquote> | }}</blockquote> | ||
<span style="color:#0070C0">(General Instructions – The main focus of these pages is the clinically significant genetic alterations in each disease type. Use [https://www.genenames.org/ <u>HUGO-approved gene names and symbols</u>] (italicized when appropriate), [https://varnomen.hgvs.org/ HGVS-based nomenclature for variants], as well as generic names of drugs and testing platforms or assays if applicable. Please complete tables whenever possible and do not delete them (add N/A if not applicable in the table and delete the examples) | <span style="color:#0070C0">(General Instructions – The main focus of these pages is the clinically significant genetic alterations in each disease type. Use [https://www.genenames.org/ <u>HUGO-approved gene names and symbols</u>] (italicized when appropriate), [https://varnomen.hgvs.org/ HGVS-based nomenclature for variants], as well as generic names of drugs and testing platforms or assays if applicable. Please complete tables whenever possible and do not delete them (add N/A if not applicable in the table and delete the examples). Please do not delete or alter the section headings. The use of bullet points alongside short blocks of text rather than only large paragraphs is encouraged. Additional instructions below in italicized blue text should not be included in the final page content. Please also see </span><u>[[Author_Instructions]]</u><span style="color:#0070C0"> and [[Frequently Asked Questions (FAQs)|<u>FAQs</u>]] as well as contact your [[Leadership|<u>Associate Editor</u>]] or [mailto:CCGA@cancergenomics.org <u>Technical Support</u>])</span> | ||
==Primary Author(s)*== | ==Primary Author(s)*== | ||
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==Clinical Features== | ==Clinical Features== | ||
Put your text here and fill in the table <span style="color:#0070C0">(''Instruction: Can include references in the table | Put your text here and fill in the table <span style="color:#0070C0">(''Instruction: Can include references in the table'') </span> | ||
{| class="wikitable" | {| class="wikitable" | ||
|'''Signs and Symptoms''' | |'''Signs and Symptoms''' | ||
| | |EXAMPLE Asymptomatic (incidental finding on complete blood counts) | ||
EXAMPLE B-symptoms (weight loss, fever, night sweats) | |||
EXAMPLE Fatigue | |||
EXAMPLE Lymphadenopathy (uncommon) | |||
|- | |- | ||
|'''Laboratory Findings''' | |'''Laboratory Findings''' | ||
| | |EXAMPLE Cytopenias | ||
EXAMPLE Lymphocytosis (low level) | |||
|} | |} | ||
<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Clinical Features|The content below was from the old template. Please incorporate above.}} | ||
Little is known about the characteristics clinical features of BCR-ABL1 positive AML. In contrast to CML, BCR-ABL1 positive AML has no antecedent hematologic disease/abnormality and no splenomegaly. Unexplained leucocytosis and/or splenomegaly point towards the diagnosis of CML myeloid blast crisis (CML-MBC) than AML<ref name=":2" />. Soupir et al. reported 16 cases of BCR-ABL1 positive AML, noting there was some overlap phenotypically and morphologically with CML myeloid blast crisis, but BCR-ABL1 positive AML cases presented less often with splenomegaly, lacked basophilia and had lower bone marrow cellularity<ref name=":3">{{Cite journal|last=Soupir|first=Chad P.|last2=Vergilio|first2=Jo-Anne|last3=Dal Cin|first3=Paola|last4=Muzikansky|first4=Alona|last5=Kantarjian|first5=Hagop|last6=Jones|first6=Dan|last7=Hasserjian|first7=Robert P.|date=2007|title=Philadelphia chromosome-positive acute myeloid leukemia: a rare aggressive leukemia with clinicopathologic features distinct from chronic myeloid leukemia in myeloid blast crisis|url=https://www.ncbi.nlm.nih.gov/pubmed/17369142|journal=American Journal of Clinical Pathology|volume=127|issue=4|pages=642–650|doi=10.1309/B4NVER1AJJ84CTUU|issn=0002-9173|pmid=17369142}}</ref>. | Little is known about the characteristics clinical features of BCR-ABL1 positive AML. In contrast to CML, BCR-ABL1 positive AML has no antecedent hematologic disease/abnormality and no splenomegaly. Unexplained leucocytosis and/or splenomegaly point towards the diagnosis of CML myeloid blast crisis (CML-MBC) than AML<ref name=":2" />. Soupir et al. reported 16 cases of BCR-ABL1 positive AML, noting there was some overlap phenotypically and morphologically with CML myeloid blast crisis, but BCR-ABL1 positive AML cases presented less often with splenomegaly, lacked basophilia and had lower bone marrow cellularity<ref name=":3">{{Cite journal|last=Soupir|first=Chad P.|last2=Vergilio|first2=Jo-Anne|last3=Dal Cin|first3=Paola|last4=Muzikansky|first4=Alona|last5=Kantarjian|first5=Hagop|last6=Jones|first6=Dan|last7=Hasserjian|first7=Robert P.|date=2007|title=Philadelphia chromosome-positive acute myeloid leukemia: a rare aggressive leukemia with clinicopathologic features distinct from chronic myeloid leukemia in myeloid blast crisis|url=https://www.ncbi.nlm.nih.gov/pubmed/17369142|journal=American Journal of Clinical Pathology|volume=127|issue=4|pages=642–650|doi=10.1309/B4NVER1AJJ84CTUU|issn=0002-9173|pmid=17369142}}</ref>. | ||
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!Notes | !Notes | ||
|- | |- | ||
| | |EXAMPLE t(9;22)(q34;q11.2)||EXAMPLE 3'ABL1 / 5'BCR||EXAMPLE der(22)||EXAMPLE 20% (COSMIC) | ||
EXAMPLE 30% (add reference) | |||
|Yes | |Yes | ||
|No | |No | ||
|Yes | |Yes | ||
| | |EXAMPLE | ||
The t(9;22) is diagnostic of CML in the appropriate morphology and clinical context (add reference). This fusion is responsive to targeted therapy such as Imatinib (Gleevec) (add reference). | The t(9;22) is diagnostic of CML in the appropriate morphology and clinical context (add reference). This fusion is responsive to targeted therapy such as Imatinib (Gleevec) (add reference). | ||
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<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Chromosomal Rearrangements (Gene Fusions)|The content below was from the old template. Please incorporate above.}} | ||
The t(9:22)(q34.1;q11.2) results in the formation of the Ph chromosome and the chimeric BCR-ABL1 fusion gene. In AML, the most common BCR-ABL1 transcripts p190 and p210 have been detected in nearly equal distribution<ref name=":2" />. Since p190 is very rare in CML (p210 transcripts in >99% of cases), the presentation with a p190 transcript is in favour of the diagnosis of AML rather than CML<ref name=":1" />. | The t(9:22)(q34.1;q11.2) results in the formation of the Ph chromosome and the chimeric BCR-ABL1 fusion gene. In AML, the most common BCR-ABL1 transcripts p190 and p210 have been detected in nearly equal distribution<ref name=":2" />. Since p190 is very rare in CML (p210 transcripts in >99% of cases), the presentation with a p190 transcript is in favour of the diagnosis of AML rather than CML<ref name=":1" />. | ||
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<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Clinical Significance (Diagnosis, Prognosis and Therapeutic Implications).|Please incorporate this section into the relevant tables found in: | ||
* Chromosomal Rearrangements (Gene Fusions) | * Chromosomal Rearrangements (Gene Fusions) | ||
* Individual Region Genomic Gain/Loss/LOH | * Individual Region Genomic Gain/Loss/LOH | ||
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==Individual Region Genomic Gain / Loss / LOH== | ==Individual Region Genomic Gain / Loss / LOH== | ||
Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: Includes aberrations not involving gene fusions. Can include references in the table. Can refer to CGC workgroup tables as linked on the homepage if applicable | Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: Includes aberrations not involving gene fusions. Can include references in the table. Can refer to CGC workgroup tables as linked on the homepage if applicable.'') </span> | ||
{| class="wikitable sortable" | {| class="wikitable sortable" | ||
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!Notes | !Notes | ||
|- | |- | ||
| | |EXAMPLE | ||
7 | 7 | ||
| | |EXAMPLE Loss | ||
| | |EXAMPLE | ||
chr7:1- 159,335,973 [hg38] | chr7:1- 159,335,973 [hg38] | ||
| | |EXAMPLE | ||
chr7 | chr7 | ||
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|Yes | |Yes | ||
|No | |No | ||
| | |EXAMPLE | ||
Presence of monosomy 7 (or 7q deletion) is sufficient for a diagnosis of AML with MDS-related changes when there is ≥20% blasts and no prior therapy (add reference). Monosomy 7/7q deletion is associated with a poor prognosis in AML (add reference). | Presence of monosomy 7 (or 7q deletion) is sufficient for a diagnosis of AML with MDS-related changes when there is ≥20% blasts and no prior therapy (add reference). Monosomy 7/7q deletion is associated with a poor prognosis in AML (add reference). | ||
|- | |- | ||
| | |EXAMPLE | ||
8 | 8 | ||
| | |EXAMPLE Gain | ||
| | |EXAMPLE | ||
chr8:1-145,138,636 [hg38] | chr8:1-145,138,636 [hg38] | ||
| | |EXAMPLE | ||
chr8 | chr8 | ||
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|No | |No | ||
|No | |No | ||
| | |EXAMPLE | ||
Common recurrent secondary finding for t(8;21) (add reference). | Common recurrent secondary finding for t(8;21) (add reference). | ||
|} | |} | ||
<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Genomic Gain/Loss/LOH|The content below was from the old template. Please incorporate above.}} | ||
AML with BCR-ABL1 carries unique genome imbalances. Nacheva et al., used array comparative genomic hybridisation (CGH) to perform a comparative study between several BCR-ABL1 positive entities. BCR-ABL1 positive AML displays characteristic of lymphoid disease (found in BCR-ABL1 positive ALL and CML): deletions of ''IKZF1'' and/or ''CDKN2A/B'' genes were recurrent findings in BCR-ABL1 positive AML as well as cryptic deletions within the immunoglobulin ''IGH'' and T cell receptor gene (''TRG alpha'') complexes<ref>{{Cite journal|last=Nacheva|first=Ellie P.|last2=Grace|first2=Colin D.|last3=Brazma|first3=Diana|last4=Gancheva|first4=Katya|last5=Howard-Reeves|first5=Julie|last6=Rai|first6=Lena|last7=Gale|first7=Rosemary E.|last8=Linch|first8=David C.|last9=Hills|first9=Robert K.|date=2013|title=Does BCR/ABL1 positive acute myeloid leukaemia exist?|url=https://www.ncbi.nlm.nih.gov/pubmed/23521501|journal=British Journal of Haematology|volume=161|issue=4|pages=541–550|doi=10.1111/bjh.12301|issn=1365-2141|pmid=23521501}}</ref>. Importantly, these aberrations were found to be absent in CML-MBC and hence they are potentially a helpful diagnostic tool for difficult cases. | AML with BCR-ABL1 carries unique genome imbalances. Nacheva et al., used array comparative genomic hybridisation (CGH) to perform a comparative study between several BCR-ABL1 positive entities. BCR-ABL1 positive AML displays characteristic of lymphoid disease (found in BCR-ABL1 positive ALL and CML): deletions of ''IKZF1'' and/or ''CDKN2A/B'' genes were recurrent findings in BCR-ABL1 positive AML as well as cryptic deletions within the immunoglobulin ''IGH'' and T cell receptor gene (''TRG alpha'') complexes<ref>{{Cite journal|last=Nacheva|first=Ellie P.|last2=Grace|first2=Colin D.|last3=Brazma|first3=Diana|last4=Gancheva|first4=Katya|last5=Howard-Reeves|first5=Julie|last6=Rai|first6=Lena|last7=Gale|first7=Rosemary E.|last8=Linch|first8=David C.|last9=Hills|first9=Robert K.|date=2013|title=Does BCR/ABL1 positive acute myeloid leukaemia exist?|url=https://www.ncbi.nlm.nih.gov/pubmed/23521501|journal=British Journal of Haematology|volume=161|issue=4|pages=541–550|doi=10.1111/bjh.12301|issn=1365-2141|pmid=23521501}}</ref>. Importantly, these aberrations were found to be absent in CML-MBC and hence they are potentially a helpful diagnostic tool for difficult cases. | ||
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==Characteristic Chromosomal Patterns== | ==Characteristic Chromosomal Patterns== | ||
Put your text here <span style="color:#0070C0">(''EXAMPLE PATTERNS: hyperdiploid; gain of odd number chromosomes including typically chromosome 1, 3, 5, 7, 11, and 17; co-deletion of 1p and 19q; complex karyotypes without characteristic genetic findings; chromothripsis | Put your text here <span style="color:#0070C0">(''EXAMPLE PATTERNS: hyperdiploid; gain of odd number chromosomes including typically chromosome 1, 3, 5, 7, 11, and 17; co-deletion of 1p and 19q; complex karyotypes without characteristic genetic findings; chromothripsis'')</span> | ||
{| class="wikitable sortable" | {| class="wikitable sortable" | ||
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!Notes | !Notes | ||
|- | |- | ||
| | |EXAMPLE | ||
Co-deletion of 1p and 18q | Co-deletion of 1p and 18q | ||
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|No | |No | ||
|No | |No | ||
| | |EXAMPLE: | ||
See chromosomal rearrangements table as this pattern is due to an unbalanced derivative translocation associated with oligodendroglioma (add reference). | See chromosomal rearrangements table as this pattern is due to an unbalanced derivative translocation associated with oligodendroglioma (add reference). | ||
|} | |} | ||
<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Characteristic Chromosomal Aberrations / Patterns|The content below was from the old template. Please incorporate above.}} | ||
In AML, BCR-ABL1 has been described together with different class II aberrations such as CBFB-MYH11, RUNX1- RUNX1T1 and PML-RARA<ref name=":2" />. In AML, BCR-ABL1 seems to cooperate with several AML-specific aberrations such as inv(16), t(8;21) and myelodysplasia-related cytogenetic aberrations<ref name=":2" /><ref>{{Cite journal|last=Bacher|first=Ulrike|last2=Haferlach|first2=Torsten|last3=Alpermann|first3=Tamara|last4=Zenger|first4=Melanie|last5=Hochhaus|first5=Andreas|last6=Beelen|first6=Dietrich W.|last7=Uppenkamp|first7=Michael|last8=Rummel|first8=Mathias|last9=Kern|first9=Wolfgang|date=2011|title=Subclones with the t(9;22)/BCR-ABL1 rearrangement occur in AML and seem to cooperate with distinct genetic alterations|url=https://www.ncbi.nlm.nih.gov/pubmed/21275954|journal=British Journal of Haematology|volume=152|issue=6|pages=713–720|doi=10.1111/j.1365-2141.2010.08472.x|issn=1365-2141|pmid=21275954}}</ref>. (For diagnostic purpose, note that inv(16) is not restricted to AML and can also be found in CML-MBC). | In AML, BCR-ABL1 has been described together with different class II aberrations such as CBFB-MYH11, RUNX1- RUNX1T1 and PML-RARA<ref name=":2" />. In AML, BCR-ABL1 seems to cooperate with several AML-specific aberrations such as inv(16), t(8;21) and myelodysplasia-related cytogenetic aberrations<ref name=":2" /><ref>{{Cite journal|last=Bacher|first=Ulrike|last2=Haferlach|first2=Torsten|last3=Alpermann|first3=Tamara|last4=Zenger|first4=Melanie|last5=Hochhaus|first5=Andreas|last6=Beelen|first6=Dietrich W.|last7=Uppenkamp|first7=Michael|last8=Rummel|first8=Mathias|last9=Kern|first9=Wolfgang|date=2011|title=Subclones with the t(9;22)/BCR-ABL1 rearrangement occur in AML and seem to cooperate with distinct genetic alterations|url=https://www.ncbi.nlm.nih.gov/pubmed/21275954|journal=British Journal of Haematology|volume=152|issue=6|pages=713–720|doi=10.1111/j.1365-2141.2010.08472.x|issn=1365-2141|pmid=21275954}}</ref>. (For diagnostic purpose, note that inv(16) is not restricted to AML and can also be found in CML-MBC). | ||
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==Gene Mutations (SNV / INDEL)== | ==Gene Mutations (SNV / INDEL)== | ||
Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: This table is not meant to be an exhaustive list; please include only genes/alterations that are recurrent and common as well | Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: This table is not meant to be an exhaustive list; please include only genes/alterations that are recurrent and common as well either disease defining and/or clinically significant. Can include references in the table. For clinical significance, denote associations with FDA-approved therapy (not an extensive list of applicable drugs) and NCCN or other national guidelines if applicable; Can also refer to CGC workgroup tables as linked on the homepage if applicable as well as any high impact papers or reviews of gene mutations in this entity.'') </span> | ||
{| class="wikitable sortable" | {| class="wikitable sortable" | ||
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!Notes | !Notes | ||
|- | |- | ||
| | |EXAMPLE: TP53; Variable LOF mutations | ||
EXAMPLE: | |||
EGFR; Exon 20 mutations | EGFR; Exon 20 mutations | ||
EXAMPLE: BRAF; Activating mutations | |||
| | |EXAMPLE: TSG | ||
| | |EXAMPLE: 20% (COSMIC) | ||
EXAMPLE: 30% (add Reference) | |||
| | |EXAMPLE: IDH1 R123H | ||
| | |EXAMPLE: EGFR amplification | ||
| | | | ||
| | | | ||
| | | | ||
| | |EXAMPLE: Excludes hairy cell leukemia (HCL) (add reference). | ||
<br /> | <br /> | ||
|} | |} | ||
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<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Gene Mutations (SNV/INDEL)|The content below was from the old template. Please incorporate above.}} | ||
Coinciding molecular events such as ''NPM1'' mutations have been reported<ref name=":1" />. | Coinciding molecular events such as ''NPM1'' mutations have been reported<ref name=":1" />. | ||
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==Genes and Main Pathways Involved== | ==Genes and Main Pathways Involved== | ||
Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: Can include references in the | Put your text here and fill in the table <span style="color:#0070C0">(''Instructions: Can include references in the table.'')</span> | ||
{| class="wikitable sortable" | {| class="wikitable sortable" | ||
|- | |- | ||
!Gene; Genetic Alteration!!Pathway!!Pathophysiologic Outcome | !Gene; Genetic Alteration!!Pathway!!Pathophysiologic Outcome | ||
|- | |- | ||
| | |EXAMPLE: BRAF and MAP2K1; Activating mutations | ||
| | |EXAMPLE: MAPK signaling | ||
| | |EXAMPLE: Increased cell growth and proliferation | ||
|- | |- | ||
| | |EXAMPLE: CDKN2A; Inactivating mutations | ||
| | |EXAMPLE: Cell cycle regulation | ||
| | |EXAMPLE: Unregulated cell division | ||
|- | |- | ||
| | |EXAMPLE: KMT2C and ARID1A; Inactivating mutations | ||
| | |EXAMPLE: Histone modification, chromatin remodeling | ||
| | |EXAMPLE: Abnormal gene expression program | ||
|} | |} | ||
<blockquote class='blockedit'>{{Box-round|title= | <blockquote class='blockedit'>{{Box-round|title=v4:Genes and Main Pathways Involved|The content below was from the old template. Please incorporate above.}} | ||
The ''BCR'' gene product has serine/threonine kinase activity and is a GTPase-activating protein for p21rac<ref>{{Cite journal|last=Maru|first=Y.|last2=Witte|first2=O. N.|date=1991|title=The BCR gene encodes a novel serine/threonine kinase activity within a single exon|url=https://www.ncbi.nlm.nih.gov/pubmed/1657398|journal=Cell|volume=67|issue=3|pages=459–468|doi=10.1016/0092-8674(91)90521-y|issn=0092-8674|pmid=1657398}}</ref>. The ''ABL1'' gene is a proto-oncogene that encodes a protein tyrosine kinase involved in a variety of cellular processes, including cell division, adhesion, differentiation, and response to stress. The activity of this protein is negatively regulated by its SH3 domain, whereby deletion of the region encoding this domain results in an oncogene<ref>{{Cite journal|last=Wang|first=Jean Y. J.|date=2014|title=The capable ABL: what is its biological function?|url=https://www.ncbi.nlm.nih.gov/pubmed/24421390|journal=Molecular and Cellular Biology|volume=34|issue=7|pages=1188–1197|doi=10.1128/MCB.01454-13|issn=1098-5549|pmc=3993570|pmid=24421390}}</ref>. The t(9,22)(q34;q11) leads to the formation of a Philadelphia chromosome and generates an active chimeric BCR-ABL1 tyrosine kinase. The fusion gene is created by juxtaposing the ''ABL1'' gene on chromosome 9 (region q34) to a part of ''BCR'' (breakpoint cluster region) gene on chromosome 22 (region q11). This is a reciprocal translocation, creating an elongated chromosome 9 (der 9), and a truncated chromosome 22 (the Philadelphia chromosome, 22q-), the oncogenic BCR-ABL1 being found on the shorter derivative 22 chromosome<ref>{{Cite journal|last=Kurzrock|first=Razelle|last2=Kantarjian|first2=Hagop M.|last3=Druker|first3=Brian J.|last4=Talpaz|first4=Moshe|date=2003|title=Philadelphia chromosome-positive leukemias: from basic mechanisms to molecular therapeutics|url=https://www.ncbi.nlm.nih.gov/pubmed/12755554|journal=Annals of Internal Medicine|volume=138|issue=10|pages=819–830|doi=10.7326/0003-4819-138-10-200305200-00010|issn=1539-3704|pmid=12755554}}</ref><ref>{{Cite journal|last=Melo|first=J. V.|date=1996|title=The diversity of BCR-ABL fusion proteins and their relationship to leukemia phenotype|url=https://www.ncbi.nlm.nih.gov/pubmed/8839828|journal=Blood|volume=88|issue=7|pages=2375–2384|issn=0006-4971|pmid=8839828}}</ref>. This gene encodes for a BCR-ABL1 fusion protein, a tyrosine kinase. Tyrosine kinase activities are typically regulated in an auto-inhibitory manner, but the BCR-ABL1 fusion gene codes for a protein that is continuously activated, causing unregulated cell division. This is a result of the replacement of the myristoylated cap region which causes a conformational change rendering the kinase domain inactive, with a truncated portion of the BCR protein<ref>{{Cite journal|last=Nagar|first=Bhushan|last2=Hantschel|first2=Oliver|last3=Young|first3=Matthew A.|last4=Scheffzek|first4=Klaus|last5=Veach|first5=Darren|last6=Bornmann|first6=William|last7=Clarkson|first7=Bayard|last8=Superti-Furga|first8=Giulio|last9=Kuriyan|first9=John|date=2003|title=Structural basis for the autoinhibition of c-Abl tyrosine kinase|url=https://www.ncbi.nlm.nih.gov/pubmed/12654251|journal=Cell|volume=112|issue=6|pages=859–871|doi=10.1016/s0092-8674(03)00194-6|issn=0092-8674|pmid=12654251}}</ref>. The enzyme is responsible for the uncontrolled growth of leukemic cells which survive better than normal blood cells. As a result of BCR/ABL1 variable splicing (fusion RNA and hybrid proteins), two transcripts p190 and p210 are found for BCR-ABL1 positive AML. | The ''BCR'' gene product has serine/threonine kinase activity and is a GTPase-activating protein for p21rac<ref>{{Cite journal|last=Maru|first=Y.|last2=Witte|first2=O. N.|date=1991|title=The BCR gene encodes a novel serine/threonine kinase activity within a single exon|url=https://www.ncbi.nlm.nih.gov/pubmed/1657398|journal=Cell|volume=67|issue=3|pages=459–468|doi=10.1016/0092-8674(91)90521-y|issn=0092-8674|pmid=1657398}}</ref>. The ''ABL1'' gene is a proto-oncogene that encodes a protein tyrosine kinase involved in a variety of cellular processes, including cell division, adhesion, differentiation, and response to stress. The activity of this protein is negatively regulated by its SH3 domain, whereby deletion of the region encoding this domain results in an oncogene<ref>{{Cite journal|last=Wang|first=Jean Y. J.|date=2014|title=The capable ABL: what is its biological function?|url=https://www.ncbi.nlm.nih.gov/pubmed/24421390|journal=Molecular and Cellular Biology|volume=34|issue=7|pages=1188–1197|doi=10.1128/MCB.01454-13|issn=1098-5549|pmc=3993570|pmid=24421390}}</ref>. The t(9,22)(q34;q11) leads to the formation of a Philadelphia chromosome and generates an active chimeric BCR-ABL1 tyrosine kinase. The fusion gene is created by juxtaposing the ''ABL1'' gene on chromosome 9 (region q34) to a part of ''BCR'' (breakpoint cluster region) gene on chromosome 22 (region q11). This is a reciprocal translocation, creating an elongated chromosome 9 (der 9), and a truncated chromosome 22 (the Philadelphia chromosome, 22q-), the oncogenic BCR-ABL1 being found on the shorter derivative 22 chromosome<ref>{{Cite journal|last=Kurzrock|first=Razelle|last2=Kantarjian|first2=Hagop M.|last3=Druker|first3=Brian J.|last4=Talpaz|first4=Moshe|date=2003|title=Philadelphia chromosome-positive leukemias: from basic mechanisms to molecular therapeutics|url=https://www.ncbi.nlm.nih.gov/pubmed/12755554|journal=Annals of Internal Medicine|volume=138|issue=10|pages=819–830|doi=10.7326/0003-4819-138-10-200305200-00010|issn=1539-3704|pmid=12755554}}</ref><ref>{{Cite journal|last=Melo|first=J. V.|date=1996|title=The diversity of BCR-ABL fusion proteins and their relationship to leukemia phenotype|url=https://www.ncbi.nlm.nih.gov/pubmed/8839828|journal=Blood|volume=88|issue=7|pages=2375–2384|issn=0006-4971|pmid=8839828}}</ref>. This gene encodes for a BCR-ABL1 fusion protein, a tyrosine kinase. Tyrosine kinase activities are typically regulated in an auto-inhibitory manner, but the BCR-ABL1 fusion gene codes for a protein that is continuously activated, causing unregulated cell division. This is a result of the replacement of the myristoylated cap region which causes a conformational change rendering the kinase domain inactive, with a truncated portion of the BCR protein<ref>{{Cite journal|last=Nagar|first=Bhushan|last2=Hantschel|first2=Oliver|last3=Young|first3=Matthew A.|last4=Scheffzek|first4=Klaus|last5=Veach|first5=Darren|last6=Bornmann|first6=William|last7=Clarkson|first7=Bayard|last8=Superti-Furga|first8=Giulio|last9=Kuriyan|first9=John|date=2003|title=Structural basis for the autoinhibition of c-Abl tyrosine kinase|url=https://www.ncbi.nlm.nih.gov/pubmed/12654251|journal=Cell|volume=112|issue=6|pages=859–871|doi=10.1016/s0092-8674(03)00194-6|issn=0092-8674|pmid=12654251}}</ref>. The enzyme is responsible for the uncontrolled growth of leukemic cells which survive better than normal blood cells. As a result of BCR/ABL1 variable splicing (fusion RNA and hybrid proteins), two transcripts p190 and p210 are found for BCR-ABL1 positive AML. | ||