Leukemia Overview and Types

Study Notes

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)

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)

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)

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)

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

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.