All-Trans Retinoic Acid

Definition:
ATRA is a differentiation agent derived from vitamin A (retinoid), used primarily to treat acute promyelocytic leukemia (APL, AML-M3).

Key Features:

1. Mechanism of Action:
   • Binds to the PML::RARA fusion protein (caused by t(15;17)).
   • Releases transcriptional repression → Forces differentiation of leukemic promyelocytes into mature granulocytes.
2. Clinical Use:
   • First-line therapy for APL (combined with arsenic trioxide (ATO) or chemotherapy).
   • Induces rapid remission (within weeks) by eliminating the differentiation block.
3. Dosing:
   • 45 mg/m²/day orally (divided into 2 doses) until complete remission.
4. Key Side Effects:
   • Differentiation syndrome (formerly retinoic acid syndrome):
     • Fever, respiratory distress, hypotension (treat with dexamethasone).
   • Hyperleukocytosis, headache, dry skin.

Example:
“A patient with APL starts ATRA + ATO, achieving remission without chemotherapy. Dexamethasone is given prophylactically to prevent differentiation syndrome.”

Why It’s Unique:

• Targeted differentiation therapy (unlike traditional cytotoxic chemo).
• Curative (>90% survival in APL when combined with ATO)