Main Ideas!- Genetic changes observed in cancer cells by cytogenomic methods:!- numerical and structural chromosomal abnormalities (translocations, deletions)!- gene amplifications!- loss of heterozygosity!- In combo w/molecular sequencing technologies, these findings have rapid accelerated an era of novel targeted therapies!!Learning Objectives!- Terms to know!- Acquired chromosome abnormality, clonal chrom abnormality, recurrent chrom abnormality, cytogenetic evolution, copy # neutral loss of heterozygosity (CNLOH), gene amplification!1) Describe the differences between a constitutional and acquired chromosome abnormality 2) Explain how an acquired translocation can result in abnormal gene function 3) Describe the t(9;22) and concepts of clonal evolution and targeted therapy. 4) Describe other acquired genetic changes associated with malignancy: LOH, gene amplification! - Acquired Clonal Chromosome Abnormality!- = acquired by cells as part of pre-malignant or malignant process!- NOT present in all cells of that person, is ONLY present in cells involved in the malignant process!- usually not present as germline finding, not due to non-disjunction or other gene mut during meiosis. Is usually an error after birth.!- 2 or more cells w/same acquired abnormality or abnormalities= Clone - Detecting and Characterizing Acquired Chromosomal Abnormalities - essential in diagnosis, plays imp. role in determining optimal therapy and in staging the malignancy!- specific recurring abnormalities in specific leukemies!- has lead to dev. of targeted cancer therapies!- Chromosome Abnormalities in Hematopoetic (blood and bone marrow) Malignancies - Acquired!- Clonal= 2 or more cells have the same abnormality!- Recurrent: the same abnormalities are seen in diff. patients w/the same type of malignancy!- Numerical: loss or gain of parts of chroms or whole chrom!- Structural: rearrangements of segments of chromosomes that result in creation of novel genes or in dysregulation of known genes!- Hemotopoetic Maligancies!- Acute:!- Lymphoid: Acute lymphoblastic (T and B cells) leukemia (ALL) - Myeloid: Acute myeloid (= all lineages involved) leukemia (AML) - Chronic:!- Lymphoid: Chronic lymphocytic leukemia (CLL) and Multiple myeloma - Myeloid: Chronic myelogenous leukemia (CML), Myelodysplastic Syndrome (MDS), Myeloproliferative Syndrome (MPS)!- Case 1: - 42 y/o woman w/pallor and fatigue, enlarged spleen, WBC= 180,000 (normal is less than 10,000)!- Bone marrow bioposy to rule out leukemia!- Karyotype: t(9;22)(q34;q11.2)!- Philadelphia chromosome!- From the bone marrow we see an acquiredtranslocation (wouldn't be in all of her bone marrow cells) and wouldn't be for ex. in her skin cells - BCR-ABL fusion gene generated on abnormal chromosome 22, Philadelphia chrom !!!!!!!!!!- Transolocation t(9;22) creates TWO gene fusions!!- BCR-ABL= Philadelphia chrom!- ABL-BCR fusion also formed, but NOT involved in gen. of leukemia!- Can use FISH to see the fusion proteins!- Normal: 2 green, 2 red!- Abnormal: 1 green, 1 red, 2 fusion red/green or yellow looking signals!- Fig. out that ABL-BCR fusion wasn't involved studying variants, you only need the BCR-ABL fusion (movement of part of chrom 9 to chrom 22) to get leukemia!!- For case 1: diagnosis= Chronic myelogenous leukemia (CML)!- due to translocation of 9,22 --> making the BCR-ABL gene!- t(9;22)(q34;q11.2)!- Derivative chrom 22= Philadelphia Chrom (Ph+)!- Translocation results in fusion of the major breakpt cluster region (BCR) in 22q11.2 to the Abelson murine leukemia virus oncogene (ABL1) in 9q34!- this translocation results in the formation of a novel (chimeric) BCR-ABL gene that encodes a protein w/altered tyrosine kinase activity!= you've created a new gene product!- Cytogenetics is used in CML to: confirm the diagnosis, help determine the stage of the disease, monitor the response to therapy!- Cytogenetic Evolution!- Acquisition of additional (secondary) abnormalities!- Freq. assoc. w/progression of disease!- Current Therapies!- Stem cell transplant!- Gleevac (Imatinib)!- therapy targeted at abnormal tyrosine kinase gen. by the t(9;22)!- from class of signal transduction inhibitors (STI)!- drug competes w/ATP for the specific binding site in kinase domain (and doesn't give phopshate that BCR-ABL needs to P-tyrosine residues on substrates)!- specificity, this is only occuring in the cancer cells !- resistance can occur!- Second generation drugs: Nilotinib, dasatinib!- Hematopoetic stem cell transplant!- Translocation can also lead to DYSREGULATION of a gene = Burkitt lymphoma (instad of forming a new chimeric gene)!- 3 translocations result of juxtaposition of the MYC oncogene w/immoglobin loci!- Case 2: - 50 y/o woman w/breast lump!- Needle core biopsy= invasive ductal carcinoma!- Sent to lab for eval of Her2 (ERBB2) status!- Her2 - aka c-erb B2!- = a proto-oncogene!- encodes a tyrosine kinase R!- ligands of HER-2 and related GF receptors= heregulins!- Amplification - Relativate increase (>2.0) in copies of Her2 gene compared with the # of #17 chromosomes present in the cell (not the same as extra copies of chrom. 17)!!!!!!!!!!!!- HER-2 Amplification!- Occurs in 25% of breast cancers!- Relationship between HER-2 amp. and poorer prognosis in invasive breast cancer!- Patients w/highest degrees of amplification have worse prognoses than patients w/lower levels!- HER-2 Amplification and therapy!- Use of recombinant anti-HER-2 monoclonal AB (Herceptin) w/cispatin --> clinical response in patients w/HER-2 overexpressing metastatic breast cancer refractory to other chemo regimens!- AKA therapy targeted to HER-2!- mAB therapy may increase radiosensitivity of overexpressing breast cancer cells!- Herceptin can increase the efficacy of other chemo agents, now being tried in neoadjuvant therapy!- Case 3:!- 22 y/o female!- Hypercellular marrow, 88.6% blasts, B lineage markers!- Normal G-banding cytogenetics, normal FISH for the recurring abnormalities - B-acute lymphoblastic leukemia!- Did an array: found 21 abnormalities in leukemia cells!- Significant copy # losses: IKZF1, PAX5, ADD3, etc.!- IKZF1: imp. in B cell development!- Study done:!- Patients w/IKEROS (IKZF1) deletions do very poorly!- can see it by arrays and now by FISH, but not in G-banding!- patients don't have the t(9;22), but have GENE EXPRESSION that resembles that translocation gene expression profile!- Philadelphia chromosome-like leukemia!- High % of patients w/high risk, acute lymphoblastic
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