Leukemia Overview and Types

Leukemia Overview

• Leukemia is a type of cancer that begins in blood-forming tissues such as bone marrow
• It involves uncontrolled proliferation of blast cells (precursor cells) in bone marrow
• Leukemia is followed by infiltration of peripheral blood and soft tissues (lymph nodes, spleen, liver, meninges, etc)
• Symptoms arise from bone marrow failure (e.g., anemia, neutropenia, thrombocytopenia) or infiltration of body organs (e.g., liver, spleen, lymph nodes)

Types of Leukemia

• Acute Leukemia: A fast-progressing cancer
  • Characterized by immature blast cells (>20% in bone marrow)
  • Classified into acute lymphoblastic leukemia (ALL) and acute myeloblastic leukemia (AML)
• Chronic Leukemia: A slowly progressing cancer
  • Classified into chronic lymphocytic leukemia (CLL) and chronic myelocytic leukemia (CML)

Acute Lymphocytic Leukemia (ALL)

• Subtypes: L1-L3
• Primarily affects children
• Definition: Uncontrolled proliferation of B or T lymphoblasts in bone marrow, leading to infiltration of peripheral blood and tissues
• Epidemiology: The most common malignant disease in children
  • Peak incidence: 2-5 years old
  • About 85% of ALL are of B type that occurs in childhood
  • About 15% of ALL are of T type that occurs in adolescents
• Clinical Features: Bone marrow failure (e.g., anemia, neutropenia, thrombocytopenia); tissue infiltration (e.g., lymphadenopathy, hepatomegaly, splenomegaly)

Acute Myeloblastic Leukemia (AML)

• Subtypes: M0-M7
• Affects adults
• Definition: Malignant proliferation of myeloid precursor cells (myeloblasts) with reduced capacity to differentiate into more mature cellular elements
• Epidemiology: Occurs at all ages. Incidence peaks after 60 years old
• FAB Classification: Categorized into 8 subtypes based on degree of maturation and lineage of leukemic blasts
• Clinical Features: Bone marrow failure (e.g., anemia, neutropenia, thrombocytopenia); soft tissue infiltration (e.g., chloroma, myeloid sarcoma)

Investigations in Acute Leukemia

• Complete Blood Count (CBC): Leucocytosis (high WBC count, potentially >100,000/mm3); anemia; thrombocytopenia.
• Peripheral Smear: Leukocytosis and presence of lymphoblasts (ALL)or myeloblasts (AML)
• Bone Marrow Examination: Hypercellular bone marrow; presence of blast cells (>20% blasts). All normal marrow elements are replaced by cancerous cells
• Cytochemistry: Identification of certain enzymes(eg. TdT)
• Immunophenotyping: Detection of antigens on the blast cells using flow cytometry (markers like CD10,19 in ALL; CD13,33 in AML)
• Cytogenetic Analysis: Identification of chromosomal abnormalities(eg. Philadelphia chromosome)
• Other Investigations: Lumbar puncture (to check for CNS involvement); testicular biopsy (for relapse detection); chest X-ray, to assess mediastinal involvement

Prognosis of Acute Leukemia

• Favorable Prognostic Markers(ALL): Age 2-10 years, low white-blood-cell count (<50,000/mm³), hyperdiploidy, or t(12;21)
• Unfavorable Prognostic Markers (ALL,AML): Age ≤2 or ≥10 years, CNS involvement, high white-blood-cell count (>50,000/mm³), presence of t(9;22)(Philadelphia chromosome)
• Overall, aggressive chemotherapy often results in remission in ~95% of childhood patients, with 75-85% surviving. AML is significantly harder to treat than ALL, with poorer remission rates and lower survival.