Haematological Malignancies: Aetiology and Genetics PDF

HAEMATOLOGICAL MALIGNANCIES: Aetiology and Genetics D R A D E B AY O A D E S H O L A M B B S , F M C PAT H , F W A C P ( L A B M E D ) L E C T U R E R / C O N S U LT A N T H A E M AT O L O G I S T ABUAD / ABUAD MS H  SY...

HAEMATOLOGICAL MALIGNANCIES: Aetiology and Genetics D R A D E B AY O A D E S H O L A M B B S , F M C PAT H , F W A C P ( L A B M E D ) L E C T U R E R / C O N S U LT A N T H A E M AT O L O G I S T ABUAD / ABUAD MS H  SYNOPSIS  Introduction  Epidemiology  Aetiology of haematologic malignancies  Genetics of haematologic malignancies  Diagnostic techniques in Haemato-oncology  Conclusion  INTRODUCTION: Haematologic malignancies  Haematologic malignancies are clonal diseases that involve haemopoietic tissues  They derive from a single cell in the bone marrow or peripheral lymphoid tissues  Most times, the tissue of origin has undergone prior genetic alteration  They include the leukaemias, lymphomas, Myelodysplastic syndrome (MDS) and Myeloproliferative neoplasms (MPN).  EPIDEMIOLOGY: Haematologic malignancies  They represent approximately 7% of all cancers  They occur with varying age, sex and geographical predilection, which all invariably affect the course of the disease EPIDEMIOLOGY: Haematologic malignancies  AETIOLOGY  Genetic background and environmental factors influence the risk of developing a malignancy  In most cases however, neither of the above is apparent, with predisposing factor remaining unknown  AETIOLOGY: Genetic factors  Genetic diseases that greatly increase the incidence of haematologic malignancies include:  Down’s syndrome  Bloom’s syndrome  Fanconi’s anaemia  Ataxia telangiectasia  Neurofibromatosis  Klinefelter’s syndrome  Wiskott-Aldrich syndrome  AETIOLOGY: Genetic factors  The above diseases mostly predispose to development of leukaemias  The lymphomas, CLL and AML also seem to show a weak familial tendency  AETIOLOGY: Environmental factors  Exposure to chemicals e.g. aromatic hydrocarbons (benzene), industrial solvents, etc.  Exposure to radiation  Drugs, especially alkylating agents (chlorambucil, melphalan, procarbazine)  Infective agents  All of the above cause varying degrees of cell injury and damage, with subsequent proliferation of aberrant, abnormal cells  AETIOLOGY: Environmental factors Infective agents: Viruses  Human T-lymphotropic virus type 1 (HTLV-1)– Adult T-cell leukaemia lymphoma (ATLL)  Epstein Barr Virus (EBV) – Endemic Burkitt’s lymphoma  Human Herpes Virus 8 (HHV 8) – Kaposi Sarcoma, Primary effusion lymphoma  HIV – Lymphoma at unusual sites Bacteria  Helicobacter pylori – Mucosa Associated Lymphoid Tissue (MALT) Lymphoma Protozoa  Malaria – Causes an alteration of host immunity, predisposes to endemic Burkitt’s lymphoma  GENETICS  When genetic mutations accumulate in cellular genes, malignant transformation results  There are essentially two groups of genes involved: Oncogenes and tumour suppressor genes  GENETICS: Oncogenes  These are genes with the potential to cause cancer proto-oncogenes  They initially existed as  Proto-oncogenes are normal genes involved in a variety of important cellular processes such as signal transduction from the exterior to the nucleus, gene activation, etc.  When the activity of these proto-oncogenes increase or when they acquire new functions (gain-of-function mutation), they transform to become oncogenes  More like a good cop becoming a bad cop.  GENETICS: Oncogenes HOW DID THESE GOOD GUYS TURN BAD? Two processes mainly:  Translocation  Duplication  GENETICS: Oncogenes TRANSLOCATION  A chromosomal abnormality resulting from exchange of parts between non-homologous chromosomes  In the process, genetic material is exchanged between the two chromosomes  This process may result in the following:  A. Formation of a chimeric fusion gene  B. Over-expression of a normal cellular gene  GENETICS: Oncogenes A. Formation of a chimeric fusion gene:  This new gene formed following genetic fusion is either dysfunctional or codes for a novel “fusion protein”  A classical example is seen in Chronic Myeloid Leukaemia (CML)  In CML, ABL1 gene on chromosome 9 is moved to the BCR gene on chromosome 22  This movement results in the formation of BCR-ABL1 fusion gene  The fusion gene in return codes for BCR-ABL1 fusion protein  This fusion protein causes excess tyrosine kinase activity, leads to excessive proliferation of cells = leukaemia.  GENETICS: Oncogenes A. Formation of a chimeric fusion gene:  Other examples include:  t(15;17) in acute myeloid leukaemia with fusion of RARα-PML gene  t(12;21) in Acute lymphoblastic leukaemia with fusion of TEL-AML1 gene  GENETICS: Oncogenes B. Over-expression of normal cellular genes:  This is seen typically in follicular lymphoma, where there is a translocation between chromosome 14 and 18  t(14;18) leads to an over-expression of the BCL-2 gene  GENETICS: Oncogenes HOW DID THESE GOOD GUYS TURN BAD? Two processes mainly:  Translocation  Duplication  GENETICS: Oncogenes DUPLICATION  Chromosomal duplication leads to extra genetic activity on the part of the chromosome duplicated  Commonly involves chromosomes 8,12,19,21 and Y  An example is Trisomy 12 seen in Chronic lymphocytic leukaemia (CLL)  GENETICS: Tumour suppressor genes  These are normal genes that serve as control mechanisms in regulating the cell cycle  They regulate entry of cells from G1 to S; S to G2, and consequently mitosis  The most common example is the p53 gene  By acquiring a loss-of-function mutation, they end up as cancer causing genes  Another case of a good cop turn bad  GENETICS: Tumour suppressor genes HOW DID THESE GOOD GUYS TURN BAD? Two processes mainly:  Point mutations  Deletions  GENETICS: Tumour suppressor genes POINT MUTATION  A genetic mutation where a single nucleotide base is changed, inserted or deleted from a sequence of DNA or RNA  Examples include  Valine617Phenylalanine (Val617Phe) mutation in the JAK 2 gene, causing myeloproliferative disease e.g. Polycythaemia, essential thrombocythaemia, Primary myelofibrosis  FLT-3 gene mutation in Acute myeloid leukaemia  GENETICS: Tumour suppressor genes HOW DID THESE GOOD GUYS TURN BAD? Two processes mainly:  Point mutations  Deletions  GENETICS: Tumour suppressor genes DELETION  Part of a chromosome gets deleted  May involve the short or long arm  Examples include:  5q- deletion in myelodysplastic syndrome (MDS)  13q14 deletion in Chronic lymphocytic leukaemia (CLL)  May also involve entire chromosomes, e.g. monosomy 7 in MDS  Deletions mostly involve chromosomes 5,6,7,11,20 and Y  Loss of multiple chromosomes is termed hypodiploidy, common in Acute lymphoblastic leukaemia (ALL)  Diagnostic Techniques in Haemato-oncology 1. Karyotyping  Involves direct morphological analysis of chromosomes from tumour cells under the microscope  Prior to this test, cells are cultured to promote cell division  Cell division is consequently arrested in metaphase using colchicine  Chromosomes are then viewed under the microscope Diagnostic Techniques in Haemato-oncology  Diagnostic Techniques in Haemato-oncology 2. Polymerase Chain Reaction (PCR)  A technique used to make many copies of a specific DNA segment  Copies of DNA sequences are exponentially amplified to generate thousands to million more copies of that particular DNA segment  It is valuable in diagnosis as well as monitoring of minimal residual disease  Diagnostic Techniques in Haemato-oncology 3. Flow cytometry  Specific antigens are expressed on the surface of normal cells, these have a characteristic profile  A different set of antigens are expressed on the surface of tumour cells, these have an aberrant (abnormal) phenotype  Flow cytometry uses antibodies labelled with different fluorochromes to recognize the pattern and intensity of expression of these antigens on the cell surface  Those cells that show an abnormal expression of surface antigens are detected as the tumour cells Diagnostic Techniques in Haemato-oncology  Diagnostic Techniques in Haemato-oncology 4. Immunohistochemistry  Uses antibodies to stain tissue sections with fluorescent markers  The stained tissue sections are then visualized under the microscope  The presence and architecture of the tumour cells can then be ascertained  Usually carried out by the Histo-pathologists Diagnostic Techniques in Haemato-oncology  Diagnostic Techniques in Haemato-oncology 5. Fluorescent in situ hybridization analysis  Involves the use of fluorescent-labelled genetic probes  These probes hybridize to specific parts of the genome  Each chromosome is labelled with a different combination of fluorescent labels  Extra copies of genetic materials, translocations e.t.c can thus be detected. Diagnostic Techniques in Haemato-oncology  Diagnostic Techniques in Haemato-oncology 6. DNA microarray platform  Used for comprehensive analysis of transcription  Known DNA probes are immobilized on a solid base and arranged in an orderly fashion  The mRNA from the tumour cell is extracted and using reverse transcriptase, it is converted to ds-cDNA and fluorescently labelled  The labelled fragments are now made to interact and bind to the complementary oligonucleotides on the immobilized DNA probes  Measurement of fluorescent intensity across the array indicates abundance of specific sequences, typically seen in malignancies. Diagnostic Techniques in Haemato-oncology  Diagnostic Techniques in Haemato-oncology 7. Gene Sequencing  Advanced techniques used to study genetic mutations responsible for disease  It is termed Next Generation Sequencing (NGS)  Can be used to study individual genes of interest, or the whole genome of the cancer  The result obtained is then compared to the germ line sequence of the patient, and the implicated mutation is consequently identified  CONCLUSION  Understanding the aetiology and genetics of haematological malignancies go long way in:  Aiding early diagnosis  Determining treatment options  Monitoring and follow up of patients ANY QUESTIONS??? The following matched are correct: A. HTLV-1 - Burkitt's lymphoma B. Human herpes-8 - Kaposi sarcoma C. Epstein-Barr virus - Adult T-cell leukaemia/lymphoma D. HIV - High grade B-cell lymphoma of brain E. Helicobacter pylori - MALT lymphoma Diagnostic methods used to study haematological malignancies include: A. Karyotypic analysis B. Flow cytometry C. High liquid performance chromatography D. Isoelectric focusing E. Polymerase Chain Reaction The following statements are true about oncogenes EXCEPT: A. They are usually derived from proto-oncogenes B. Derived following a loss of function of proto-oncogenes C. Translocation and duplication can result in their formation D. PML-RARα is an example E. They have minimal potential of causing cancers MANAGEMENT OF HAEMATOLOGIC MALIGNANCIES: AN OVERVIEW  MANAGEMENT  HISTORY  PHYSICAL EXAMINATION  INVESTIGATIONS  TREATMENT  FOLLOW UP  PROGNOSIS  DIAGNOSTIC INVESTIGATIONS  Full blood count and differentials  Peripheral blood film  Bone marrow aspiration and biopsy  Cytochemistry  Immunophenotyping  Cytogenetics  Molecular Genetics  SUPPORTIVE INVESTIGATIONS  Clotting profile (PT, APTT)  Serum U/E, Cr  Blood sugar  Liver function tests  Uric acid, Ca2+, Phosphate  Background viral serology (medico-legal implications)  Sepsis work up  Radiological evaluation (X-ray, USS, CT, PET scan)  TREATMENT : SUPPORTIVE  Counselling  Reproductive issues  Nutritional support  Determine baseline performance status of patient  Insertion of a central venous catheter  Intravenous fluid administration  Blood and blood product support  Anti-infective agents (prophylaxis)  Anti-uric acid agents  Analgesics  TREATMENT : DEFINITIVE  Combination cytotoxic chemotherapy  Radiation  Surgery – where applicable