22:50
Leukemias: Pathology review
Osmosis from Elsevier
Overview
This video explains the pathology of leukemias, a group of cancers characterized by the uncontrolled proliferation of immature white blood cells. It differentiates leukemias from lymphomas and details the genetic mutations that can cause them. The video categorizes leukemias into acute (AML, ALL) and chronic (CML, CLL, Hairy Cell Leukemia) based on the maturity of the affected cells and their progression rate. It also covers the distinct symptoms, diagnostic methods, and specific subtypes of each leukemia, using patient case examples to illustrate the concepts.
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Chapters
- Leukemia is the uncontrolled growth of immature white blood cells (blast cells) in the bone marrow or blood.
- Leukemias differ from lymphomas, which form solid tumors in lymphatic tissues.
- Genetic mutations, such as chromosomal deletions, trisomies, and translocations, are common causes of leukemia.
- Abnormal cells crowd out normal blood cells, leading to decreased immune function (infections), anemia, thrombocytopenia, and leukopenia.
- Leukemic cells can infiltrate organs like the liver, spleen, and lymph nodes, causing organ enlargement and swelling.
Understanding the fundamental cause and mechanism of leukemia is crucial for recognizing its broad impact on the body's blood-forming and immune systems.
Mike, a 65-year-old man, presents with easy bruising and rapid deterioration due to low platelets and bleeding, illustrating the consequences of bone marrow crowding.
- Leukemias are classified by cell type: myeloid (affecting monocytes, granulocytes) or lymphoid (affecting T cells, B cells).
- Leukemias are also classified by progression speed: acute (rapid, immature blast cells) or chronic (slow, less mature but dysfunctional cells).
- Acute leukemias include Acute Myeloid Leukemia (AML) and Acute Lymphoblastic Leukemia (ALL).
- Chronic leukemias include Chronic Myeloid Leukemia (CML), Chronic Lymphocytic Leukemia (CLL), and Hairy Cell Leukemia (HCL).
This classification system is essential for guiding diagnosis, treatment strategies, and predicting patient outcomes, as acute and chronic leukemias have different clinical courses.
Luke, a 5-year-old, presents with recurrent infections and anemia, suggesting an acute leukemia, while Mia, a 40-year-old, has fatigue and splenomegaly, hinting at a chronic leukemia.
- AML is more common in older adults and often linked to specific translocations (e.g., t(15;17)) or myelodysplastic syndromes.
- ALL is more common in children and associated with translocations (e.g., t(12;21), t(9;22)/Philadelphia chromosome) and Down syndrome.
- Acute Promyelocytic Leukemia (APL), a subtype of AML, is caused by t(15;17) and treated with all-trans retinoic acid.
- ALL can be B-cell or T-cell type; B-cell ALL is more common and can also be called lymphoblastic lymphoma.
- Risk factors for acute leukemia include radiation and chemotherapy exposure.
Understanding the specific genetic underpinnings and patient demographics for AML and ALL is critical for accurate diagnosis and targeted therapy.
Mike's bone marrow biopsy showing over 30% blast cells with Auer rods is characteristic of AML, specifically APL due to the Auer rods.
- CML is typically caused by the Philadelphia chromosome (t(9;22)), creating the BCR-ABL fusion gene that drives uncontrolled myeloid cell proliferation.
- CML can progress to AML in a 'blast crisis' if further mutations occur.
- CLL, common in the elderly, involves mutations affecting lymphocytes (especially B cells), leading to their accumulation and potential transformation into aggressive lymphomas.
- CLL can cause autoimmune complications like immune thrombocytopenia and hemolytic anemia.
- Hairy Cell Leukemia (HCL) is a rare chronic leukemia often caused by a BRAF mutation, characterized by B cells with hair-like projections, bone marrow fibrosis, and significant splenomegaly.
The distinct molecular drivers and clinical behaviors of CML, CLL, and HCL necessitate specific diagnostic approaches and targeted treatments, such as tyrosine kinase inhibitors for CML.
Mia's presentation with increased granulocytes and immature myeloid cells, coupled with a low LAP score, strongly suggests CML in its chronic phase.
- Common symptoms across leukemias include fatigue (anemia), bleeding (thrombocytopenia), and infections (leukopenia).
- Bone pain, abdominal fullness (hepatosplenomegaly), and lymphadenopathy are also frequent.
- Diagnosis involves peripheral blood smears (identifying blast cells, Auer rods, smudge cells, or hairy projections), bone marrow biopsies (quantifying blast percentage), immunophenotyping (cell markers), and genetic testing (e.g., Philadelphia chromosome).
- Distinguishing AML from ALL relies on identifying myeloblasts vs. lymphoblasts and specific cell markers.
- Low LAP score differentiates CML from leukemoid reactions; specific genetic tests confirm CML and CLL diagnoses.
Accurate diagnosis relies on a multi-faceted approach combining clinical presentation with laboratory and genetic findings to precisely identify the leukemia subtype.
Mike's bleeding from puncture sites, low platelets, prolonged PT/PTT, decreased fibrinogen, elevated D-dimer, and schistocytes on smear point to Disseminated Intravascular Coagulation (DIC), a complication often seen in APL.
Key takeaways
- Leukemia arises from uncontrolled proliferation of immature white blood cells, disrupting normal blood cell production and immune function.
- The distinction between acute (rapid, blast cells) and chronic (slow, dysfunctional mature cells) leukemias is fundamental to their management.
- Specific genetic mutations, like the Philadelphia chromosome in CML or t(15;17) in APL, are key diagnostic and therapeutic targets.
- Patient age is a significant factor in differentiating common types of acute leukemia (AML in older adults, ALL in children).
- Diagnostic tools like blood smears, bone marrow biopsies, immunophenotyping, and genetic tests are essential for precise leukemia classification.
- Leukemias can lead to serious complications such as anemia, bleeding disorders (DIC), increased infections, and organ infiltration.
- Understanding the molecular basis of leukemia allows for the development of targeted therapies, such as tyrosine kinase inhibitors for CML.
Key terms
LeukemiaBlast cellsMyeloid leukemiaLymphoid leukemiaAcute leukemiaChronic leukemiaAML (Acute Myeloid Leukemia)ALL (Acute Lymphoblastic Leukemia)CML (Chronic Myeloid Leukemia)CLL (Chronic Lymphocytic Leukemia)Philadelphia chromosomeAuer rodsImmunophenotypingLeukopeniaThrombocytopeniaAnemiaHepatosplenomegalyLymphadenopathyDIC (Disseminated Intravascular Coagulation)LAP score
Test your understanding
- How does the uncontrolled proliferation of blast cells in leukemia lead to symptoms like frequent infections, easy bruising, and fatigue?
- What are the key differences in cell maturity and progression rate between acute and chronic leukemias?
- How does the presence of the Philadelphia chromosome specifically contribute to the development and progression of Chronic Myeloid Leukemia (CML)?
- What diagnostic findings, such as Auer rods or specific cell surface markers, help differentiate between AML and ALL?
- Why is a low Leukocyte Alkaline Phosphatase (LAP) score significant in diagnosing CML and distinguishing it from a leukemoid reaction?