acute myeloid leukemia
Summary
Acute myeloid leukemia (AML) is a clonal malignancy of myeloid precursor cells characterized by ≥20% blasts in bone marrow or blood, leading to bone marrow failure. It predominantly affects adults (median age ~65) and presents with fatigue, infections, and bleeding due to pancytopenia. Diagnosis relies on marrow biopsy, flow cytometry, and cytogenetic/molecular testing.
Detail
AML arises from clonal proliferation of immature myeloid blasts that fail to differentiate, crowding out normal hematopoiesis and causing anemia, neutropenia, and thrombocytopenia. Risk factors include prior chemotherapy (alkylating agents, topoisomerase II inhibitors), radiation exposure, myelodysplastic syndrome, Down syndrome, and certain genetic syndromes (Fanconi anemia). Clinical features stem from marrow failure: fatigue/pallor (anemia), fever/infections (neutropenia), and bleeding/bruising/petechiae (thrombocytopenia); gum hypertrophy and skin infiltration (chloromas) are classic in monocytic subtypes (M4/M5). Acute promyelocytic leukemia (APL, M3) is a distinct subtype with t(15;17) PML-RARA fusion, presenting with DIC and treated with ATRA plus arsenic trioxide, avoiding cytotoxic induction chemotherapy when possible due to rapid remission with differentiation therapy. Diagnosis requires bone marrow blasts ≥20% (vs ALL's lymphoblasts), confirmed via flow cytometry (myeloid markers: CD13, CD33, CD117, myeloperoxidase positivity) and cytogenetics. Peripheral smear may show myeloblasts with Auer rods (azurophilic granular inclusions), pathognomonic for AML, especially APL. Cytogenetic/molecular abnormalities guide prognosis: favorable (t(15;17), t(8;21), inv(16)), intermediate (normal karyotype, NPM1 mutation without FLT3-ITD), and poor (complex karyotype, FLT3-ITD, TP53 mutations, monosomy 5/7). Treatment involves induction chemotherapy (typically "7+3": cytarabine + anthracycline) to achieve remission, followed by consolidation (high-dose cytarabine) or allogeneic stem cell transplant based on risk stratification. FLT3 inhibitors (midostaurin) and targeted agents (venetoclax, IDH inhibitors) are used in specific molecular subtypes. Complications include tumor lysis syndrome, DIC (especially APL), and infections from prolonged neutropenia. AML is distinguished from ALL by myeloperoxidase positivity, CD13/CD33 expression, and Auer rods, whereas ALL shows TdT positivity and lymphoid markers (CD19, CD10).
Sources
- First Aid for the USMLE Step 1
- Robbins Basic Pathology
- UpToDate: Acute myeloid leukemia
- Harrison's Principles of Internal Medicine
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