## Acute Promyelocytic Leukemia (APL) — t(15;17) Management **Key Point:** APL with t(15;17) is a medical emergency with unique treatment paradigm distinct from other AML subtypes. ### Molecular Basis The t(15;17) translocation produces the PML-RARA fusion gene, which encodes an aberrant retinoic acid receptor. This fusion protein blocks differentiation and causes severe coagulopathy (DIC). ### First-Line Induction Regimen | Component | Role | Mechanism | |-----------|------|----------| | **ATRA** | Differentiating agent | Binds fusion protein, restores normal transcription, forces maturation | | **Arsenic trioxide (ATO)** | Synergistic cytotoxic | Degrades PML-RARA fusion protein via proteasomal pathway | **High-Yield:** The combination of ATRA + ATO achieves **90–95% complete remission** with cure rates >80% in newly diagnosed APL — superior to traditional anthracycline-based chemotherapy. ### Clinical Pearl - ATRA monotherapy causes **ATRA syndrome** (fever, respiratory distress, weight gain, pulmonary infiltrates) in 5–30% of patients → managed with dexamethasone prophylaxis or early intervention. - ATO is added to reduce ATRA syndrome risk and improve overall survival. - Early recognition of t(15;17) is critical: initiate ATRA + ATO **before** cytogenetics confirm, given the high mortality from DIC if delayed. ### Supportive Care - Aggressive coagulopathy management (fresh frozen plasma, cryoprecipitate, platelets). - All-trans retinoic acid syndrome monitoring. [cite:Harrison 21e Ch 110]
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