© 2014, The Japanese Society of Hematology. Therapy-related myeloid neoplasms (t-MN) have a common origin in prior cytotoxic therapy and/or radiation. These neoplasms include therapy-related acute myeloid leukemia, myelodysplastic syndrome (t-MDS), and myelodysplastic/myeloproliferative neoplasms (t-MDS/MPN). Myeloid sarcoma (MS), on the other hand, is a rare disease manifesting as an extramedullary collection of immature cells of myeloid lineage. Rarer still is therapy-related MS (t-MS), which has not been adequately studied due to its rarity and its lack of recognition as a unique entity among other t-MN. Here, we report what is to our knowledge the first case series of t-MS, with the aim of investigating and establishing salient clinicopathological and molecular features of this entity.