AML

• Mostly in adults 15-39 YOA; only 20% of childhood leukemia

• Chloromas may be seen and they represent tumorous masses of leukemic cells in soft tissues

• Infiltration of the gums is characteristic of M4 and M5

• Morphological and cytochemical classification (FAB)

  • M0: minimally differentiated

    • 2-3% of AML

    • Blasts like cytologic and cytochemical markers or myeloblasts, but express myeloid lineage Ags

  • M1: AML without differentiation

    • ~20% of AML

    • Myeloblasts predominate

    • Distinct nucleoli, few granules or Auer rods

    • Myeloperoxidase and/or Sudan black +

  • M2: AML with differentiation

    • 30-40% of AML

    • Myeloblasts and promyelocytes (type II blasts) predominate

    • Auer rods are often present

    • SB and/or MP ++

    • Better prognosis if t(8;21) is present

  • M3a: acute promyelocytic leukemia

    • 5-10% of AML; more common in Hispanics

    • Hypergranular promyelocytes, often with many Auer rods per cell

    • May have reniform or bilobed nucleus

    • SB and MP +++

    • Often develop DIC

    • The t(15;17) is characteristic

  • M3b: microgranular variant

    • Similar to M3a, but greater risk for DIC

    • Also associated with t(15;17)

  • M4: acute myelomonocytic leukemia

    • 15-20% of AML

    • Seen myeloblasts (resemble M2) and monoblasts (bidifferentiation)

    • MP and nonspecific esterase ++

    • M4eo

      • This is marrow eosinophilia and abnormalities of chromosome 16

      • Associated with good prognosis, but frequent CNS involvement

  • M5a: acute monoblastic leukemia

    • ~10% of AML

    • Undifferentiated blasts that look like M1 predominate

    • MP , NSE +/++

  • M5b: acute promonocytic variant

    • See mostly cells that look like monocytes (promonocytes)

    • MP , NSE ++/+++

  • M6: acute erythroleukemia (diGuglielmo’s disease)

    • ~5% AML

    • Multinucleated, megaloblastoid erythroblasts predominate; also some myeloblasts

    • Myeloblasts MP+, erythroblasts PAS+

  • M7: acute megakaryocytic leukemia

    • ~1% of AML

    • See pleomorphic undifferentiated blasts that may have cytoplasmic budding

    • Marrow is often fibrotic

    • Megakaryoblasts react with platelet-associated Abs and platelet peroxidase; vWF (+)

  • Rare variants: mixed lineage AML (myeloid + lymphoid) – eosinophilic/basophilic

Category: Medical Subject Notes , Pathology Notes