Leukemia - General Overview

I’ll give you a structured overview of leukemias and related lymphoid malignancies, and then explain Ann Arbor, Kiel, and the B- vs T-cell differences.

Leukemia – General Overview

Definition:Leukemias are malignant neoplasms of hematopoietic cells originating in the bone marrow and spilling into peripheral blood. They disrupt normal hematopoiesis and immunity.

Main categories (based on course and lineage):

1. By clinical course

   • Acute: Rapid onset, immature “blast” cells dominate. (e.g., AML, ALL)

   • Chronic: Slower course, more mature cell types. (e.g., CML, CLL)

2. By cell lineage

   • Myeloid: Granulocytes, monocytes, erythrocytes, megakaryocytes.

   • Lymphoid: B-cells, T-cells, NK-cells.

Major groups:

• Acute lymphoblastic leukemia (ALL) – children, young adults, precursor B or T cells.

• Acute myeloid leukemia (AML) – adults, blasts from myeloid lineage.

• Chronic lymphocytic leukemia (CLL) – elderly, usually small mature B-cells.

• Chronic myeloid leukemia (CML) – driven by BCR-ABL1 fusion (t(9;22) Philadelphia chromosome).

B-cells vs T-cells in Leukemia/Lymphoma

• B-cells:

  • Originate in bone marrow, undergo V(D)J recombination, somatic hypermutation, class switching.

  • Leukemias/lymphomas: CLL, B-ALL, DLBCL, multiple myeloma.

  • Express CD19, CD20, CD79a, CD10 (precursors).

• T-cells:

  • Originate in thymus (positive/negative selection).

  • Leukemias/lymphomas: T-ALL, peripheral T-cell lymphoma, Sézary syndrome.

  • Express CD3, CD4, CD8, TCR (αβ or γδ).

Clinical difference:

• B-cell leukemias often show lymphadenopathy, marrow infiltration, paraproteinemia (plasma cell stage).

• T-cell leukemias may present with mediastinal masses (thymus), skin lesions, more aggressive course.

Ann Arbor Classification

This is actually not for leukemia but for lymphomas (both Hodgkin and non-Hodgkin). It classifies disease extent/stage, not cell type:

• Stage I: Single lymph node region or single extralymphatic organ.

• Stage II: ≥2 lymph node regions on the same side of diaphragm.

• Stage III: Lymph nodes on both sides of diaphragm, possibly spleen.

• Stage IV: Diffuse/disseminated involvement of extralymphatic organs (e.g., bone marrow, liver).

Modifiers:

• A/B: Absence/presence of “B symptoms” (fever, night sweats, weight loss).

• E: Extralymphatic involvement.

• S: Splenic involvement.

Hodgkin Lymphoma

• Malignancy of Reed–Sternberg cells (large atypical B-cells).

• Subtypes (WHO classification):

  • Nodular sclerosis

  • Mixed cellularity

  • Lymphocyte-rich

  • Lymphocyte-depleted

  • Nodular lymphocyte-predominant (special case, CD20+).

Differs from leukemia:

• HL is usually localized to lymph nodes at diagnosis and spreads in a contiguous pattern, whereas leukemias are marrow-based and disseminated early.

Kiel Classification

• Historical system (1974; revised 1988, mainly used in Europe pre-WHO).

• Applied to non-Hodgkin lymphomas (not leukemias directly).

• Divided into:

  • Low-grade lymphomas (indolent): e.g., lymphocytic, follicular, centrocytic.

  • High-grade lymphomas (aggressive): e.g., lymphoblastic (T- and B-), immunoblastic, centroblastic.

Basis:

• Morphology (microscopy) of lymph node biopsies.

• Immunophenotype (B vs T lineage).

Later replaced by REAL (1994) and WHO classification (2001, 2008, 2016, 2022), which integrate morphology, immunophenotyping, genetics, and clinical features.

Putting It All Together

• Leukemia = marrow/blood malignancy (ALL, AML, CLL, CML).

• Lymphoma = solid lymphoid tissue malignancy (Hodgkin, non-Hodgkin).

• Ann Arbor = staging system for lymphoma (not leukemia).

• Kiel = historical classification for NHL (replaced by WHO).

• B vs T cell difference = immunophenotype and clinical behavior.

• Hodgkin vs non-Hodgkin = Reed–Sternberg cells, spread pattern, therapeutic approach.

✅ In short:

• Leukemias are systemic from the start; classified by lineage (myeloid vs lymphoid) and acuity (acute vs chronic).

• Lymphomas are classified by histology/immunophenotype (Kiel, WHO) and staged by Ann Arbor.

• B- vs T-cells define immunophenotype, markers, clinical features.

• Hodgkin Lymphoma is its own entity with Reed–Sternberg cells and special clinical behavior.