Acute promyelocytic leukemia with a smoldering course associated with therapy-related myelodysplastic syndrome.

Acute promyelocytic leukemia (APL) may appear rarely as a late complication of the treatment of other primary cancers. Therapy-related APL (tAPL) differs from de novo APL in epidemiological and clinical parameters but shares common molecular signatures and does not differ in survival end- points. We describe a 67-year-old female patient who presented with an atypical course of tAPL. Atypical features in this patient's course included a preceding therapy-related myelodysplastic syndrome (MDS) with a slowly expanding pathological promyelocyte clone. Following treatment with all-trans-retinoic acid and arsenic trioxide, the patient achieved complete clinical, morphological and molecular remission. Review of the pertinent literature highlights the rarity of MDS transforming into APL, although dysplasia has been shown to be a possible feature of tAPL. MDS may be an underdiagnosed stage in tAPL leukomogenesis. This case also underscores the complexity of clinical decision-making in the context of tAPL.