Haematological Malignancies Notes

Learning Outcomes

• Knowledge of malignancies affecting myeloid and lymphoid lineages, including specific disease subtypes, genetic mutations, and clinical presentations.

• Knowledge of pathologic features associated with common myeloid and lymphoid malignancies, enabling accurate diagnosis and classification.

• Understanding of lab methods for diagnosing haematological malignancies, including their principles, applications, and limitations.

• Understanding of lab methods providing prognostic information in haematological malignancies, guiding treatment strategies and predicting patient outcomes.

Overview of Haemato-oncology

• Haemato-oncology: Study of cancers of the haematopoietic system, including leukaemia, lymphoma, myeloma, and myelodysplastic syndromes.

• Oncogenic mutation: Occurs within a haematopoietic cell, leading to uncontrolled proliferation and creating a malignant clone. These mutations can affect genes involved in cell growth, differentiation, and apoptosis.

• Malignant clone: Negatively affects haematopoiesis by crowding out normal cells, disrupting cytokine signaling, and impairing immune function.

• Impact: Inability to produce functional red and white blood cells is fatal, leading to anaemia, infection, and bleeding complications.

Clonality

• Clonal cells: Contain identical DNA copies, arising from a single mutated cell. This uniformity is a hallmark of malignancy.

• Initiation: Starts with a mutation in a single cell, such as a point mutation, deletion, translocation, or epigenetic modification. Driver mutations confer a selective growth advantage.

• Inheritance: All daughter cells inherit the same genetic mutation, perpetuating the malignant clone and contributing to disease progression.

Malignant Features

Haematological malignancies share common characteristics:

• Failure to produce effector cells: Malignant cells often fail to differentiate into functional immune cells, compromising the body's ability to fight infection.

• Accumulation of cells at intermediate differentiation stages (maturational arrest): Malignant cells may be blocked at specific stages of development, leading to an accumulation of immature blasts in the bone marrow and peripheral blood.

• Increased proliferation rate: Malignant cells divide rapidly, overwhelming normal haematopoiesis and leading to organ infiltration and systemic symptoms.

• Failure to undergo apoptosis: Malignant cells evade programmed cell death, contributing to their accumulation and resistance to therapy.

Lineage Classifications

• Myeloid- Leukaemia

  • Myelodysplastic syndrome

  • Myeloproliferative neoplasm

• Lymphoid- Leukaemia

  • Lymphoma

  • Multiple myeloma

Leukaemia

• Definition: Presence of malignant cells in peripheral blood and bone marrow, disrupting normal haematopoiesis and causing cytopenias.

• Classification: By lineage (myeloid, lymphoid) and rate of progression (acute, chronic). - Myeloid: Affecting red blood cells, granulocytes, monocytes, and platelets, as well as their precursors.

  • Lymphoid: Affecting lymphocytes (B, T, NK cells) and their precursors.

• Acute Leukaemia- Characterized by:- Accumulation of immature cells ('blasts'): Blasts proliferate uncontrollably, replacing normal bone marrow elements.
  - Increased proliferation rate: Rapid disease progression requiring immediate treatment.
  - Clinically aggressive disease: Symptoms develop rapidly and can be life-threatening.
  - Maturational arrest: Blasts fail to differentiate into mature cells, impairing normal blood cell production.

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• Chronic Leukaemia- Characterized by:- Failure to undergo apoptosis: Malignant cells accumulate slowly over time.
  - Less aggressive disease: Symptoms develop gradually, and patients may be asymptomatic for years.

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• Bone Marrow (BM) Tumour- Site: BM is the site of haematopoiesis and the tumour, leading to disruption of normal blood cell production.

  • Mechanism: Increasing numbers of malignant cells in the BM, crowding out normal cells and altering the BM microenvironment.

  • Effect: Suppression of normal haematopoiesis and the 'normal' clone, resulting in anaemia, thrombocytopenia, and neutropenia.

Lymphoma

• Definition: Lymphoid malignancy forming a solid tumour within secondary lymphoid organs, such as lymph nodes, spleen, and thymus.

• Cell type: Malignant cells can be B, T, or NK cells, each with distinct characteristics and clinical manifestations.

• Classification: By rate of progression.- Low Grade:- Slowly proliferating malignant cells, often with indolent clinical behaviour.

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  • High Grade:- Rapidly proliferating malignant cells, requiring aggressive treatment.

    • Clinically aggressive disease: Symptoms develop quickly and can be life-threatening.

• Hodgkin Lymphoma- Defined by the presence of Reed-Sternberg cells, which are mature B cell malignancies with characteristic morphology and immunophenotype.

  • These cells fail to undergo apoptosis, contributing to their accumulation in lymph nodes.

Reed-Sternberg Cell

• Diagnostic for Hodgkin Lymphoma, characterized by their large size, multinucleated appearance, and expression of CD30 and CD15.

Non-Hodgkin Lymphoma

• Definition: Diverse group of malignant diseases, involving mature B, T, or NK cell malignancies with varied clinical presentations and prognoses.

• Key feature: Failure to undergo apoptosis, leading to the accumulation of malignant cells in lymphoid tissues.

• Leukaemic Phase- Malignant cells enter peripheral circulation and appear in the BM, blurring the distinction between lymphoma and leukaemia.

  • Proliferation continues within the BM, further disrupting normal haematopoiesis.

• Marrow Infiltration- Suppresses haematopoiesis and the 'normal' clone, resulting in cytopenias and bone marrow failure.

Myelodysplastic Syndrome

• Classification: Myeloid malignancy characterized by ineffective haematopoiesis and a high risk of transformation to acute myeloid leukaemia (AML).

• Mechanism: Increased proliferation of precursor cells in the bone marrow, leading to maturational arrest and abnormal cell morphology (dysplasia).

• Effect: Premature cell death (ineffective haematopoiesis), resulting in cytopenias and increased risk of infection and bleeding.

• Bone Marrow: Hyper-cellularity but with suppression of normal haematopoiesis and the 'normal' clone, particularly affecting erythroid cells, leading to anaemia.

Multiple Myeloma

• Classification: Lymphoid malignancy involving mature B cells (plasma cells) that produce monoclonal antibodies (paraproteins).

• Key features:- Increased monoclonal antibody concentrations in the blood, detectable by serum protein electrophoresis and immunofixation.

  • Increased proliferation and failure to undergo apoptosis, leading to the accumulation of malignant plasma cells in the bone marrow.

  • BM Accumulation

  • Suppression of haematopoiesis and the 'normal' clone, resulting in anaemia, hypercalcemia, renal insufficiency, and bone lesions (CRAB).

Myeloproliferative Neoplasms

• Classification: Myeloid lineage malignancies characterized by clonal expansion of haematopoietic stem cells and increased production of one or more blood cell types.

• Key feature: Increased rate of proliferation.- Polycythemia: Accumulation of mature erythrocytes, leading to increased blood viscosity and risk of thrombosis.

  • Essential thrombocythemia: Accumulation of megakaryocytes, resulting in elevated platelet counts and risk of bleeding or thrombosis.

• Effect :Suppression of haematopoiesis and the 'normal' clone, leading to cytopenias and bone marrow fibrosis.

Laboratory Investigations

• Bone Marrow Sampling- Necessity determined by clinical symptoms and initial FBC (Full Blood Count) results, backed up by blood film examination to evaluate cell morphology and identify abnormalities.

BM Samples

Two types:

• Aspirate- BM film: Morphological assessment of cells, including cell size, shape, nuclear features, and cytoplasmic granules.

  • Flow cytometry: Cell marker analysis to identify cell lineage, differentiation stage, and clonality.

  • Cytogenetics: Assessment of chromosomal abnormalities, such as translocations, deletions, and aneuploidies.

  • Minimal residual disease (MRD) monitoring to detect persistent disease after treatment.

• Trephine biopsy- Processed for histology to assess bone marrow architecture.

  • Histopathology examination to evaluate cellularity, fibrosis, and infiltration by malignant cells.

  • Immunohistochemistry: Cell marker analysis to confirm cell lineage and identify specific proteins expressed by malignant cells.

Assessment of Cell Morphology

• BM film analysis for cell morphology assessment, including examination of Wright-Giemsa-stained smears under a microscope.

BM Trephine

• Assessment of BM architecture and cell morphology, providing valuable information about disease infiltration and marrow fibrosis.

• Diagnostic for haematological malignancies, aiding in the classification and staging of disease.

• Suggestive of cell lineage and maturation stage but requires confirmation via further laboratory testing, such as flow cytometry and cytogenetics.

Flow Cytometry

• Method: Cells labelled with fluorescent antibodies to detect specific cell markers (proteins) expressed on their surface or within the cytoplasm.

• Analysis: Staining patterns confirm cell lineage and developmental stage, allowing for the identification of malignant cells and their immunophenotype.

• Applications:- Differentiates between myeloid and lymphoid cells, aiding in the diagnosis of leukaemia and lymphoma.

  • Differentiates between species of cells.

  • Differentiates between intermediate stages of development of cells, helping to identify maturational arrest and clonal abnormalities.

• CONFIRMS DIAGNOSIS

Cytogenetics

• Purpose: Assessment of karyotype, investigation of chromosomal abnormalities that are characteristic of specific haematological malignancies.

• Significance: Clonal diseases show the same abnormality in all cells; this is a PROGNOSTIC INDICATOR, providing information about disease aggressiveness and response to therapy.

Karyotype

• Normal state: 23 pairs of chromosomes (46 total) per cell, arranged in a specific banding pattern.

• Metaphase: Chromosomes are condensed and visible under light microscopy, allowing for analysis of their number and structure.

• Euploid: Somatic cell with 46 chromosomes, indicating a normal chromosomal complement.

• Aneuploidy: Loss or gain of chromosomes, resulting in an abnormal chromosome number.

• Examples of Aneuploidy- Monosomy:loss of a chromosome (e.g Monosomy 7), often associated with myeloid malignancies.

  • Trisomy: Gain of a chromosome (e.g Trisomy 18), commonly seen in lymphoid malignancies.

Translocation

• Process: Exchange of genetic material between chromosomes, resulting in the fusion of genes and the production of novel proteins.- Example: BCR-ABL translocation, creating the Philadelphia chromosome (Ph+), which is characteristic of chronic myeloid leukaemia (CML).
  - High prognostic significance, indicating sensitivity to tyrosine kinase inhibitors (TKIs).

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  • Mechanism:- Occurs via exchange between chromosome 9 (BCR) and chromosome 22 (C-ABL), resulting in the fusion of the BCR and ABL genes.

    • Results in a fusion protein with constitutive tyrosine kinase activity, driving uncontrolled cell proliferation.

    • $t(9;22)(q34.1;q11.2)$

Minimal Residual Disease (MRD)

• Definition: Detection of tumour cells during/after treatment, even at very low levels, indicating persistent disease and risk of relapse.

• Significance: High prognostic value, indicating efficacy of treatment and predicting long-term outcomes.

• Methods:- Molecular methods (e.g., PCR) to detect specific gene mutations or fusion transcripts.

  • Rare cell detection via flow cytometry to identify malignant cells based on their immunophenotype.

Recommended Reading

• Fundamentals of Biomedical Science - Haematology by Gary Moore, Gavin Knight & Andrew Blann, 2016; Oxford University Press, Oxford, UK. Second edition. Chapter 9 – Introduction to haematological malignancies.