abstract:Retinoic acid syndrome (RAS) is a potentially life threatening complication observed in patients with acute promyelocytic leukemia (APML) and first thought to be specifically associated with all-trans retinoic acid (ATRA) (also known as tretinoin) treatment. Subsequently it was recognized that so-called RAS appeared in APML patients who had been treated with another highly efficacious drug, arsenic trioxide, and yet did not appear in patients treated with tretinoin for other disorders.