Phenasen is indicated for induction of remission, and consolidation in adult patients with:• Newly diagnosed low-to-intermediate risk acute promyelocytic leukaemia (APL) (white blood cell count, ≤ 10x1000/µl) in combination with all-trans-retinoic acid (ATRA)• Relapsed/refractory acute promyelocytic leukaemia (APL)(Previous treatment should have included a retinoid and chemotherapy) characterised by the presence of the t(15;17) translocation and/or the presence of the Pro-Myelocytic Leukaemia/Retinoic-Acid-Receptor-alpha (PML/RAR-alpha) gene. The response rate of other acute myelogenous leukaemia subtypes to arsenic trioxide has not been examined.