Refractory Anemia with Ring Sideroblasts Associated with Marked Thrombocytosis Complicated by a Parasternal Granulocytic Sarcoma

Refractory anemia with ring sideroblasts associated with marked thrombocytosis (RARS-T) and granulocytic sarcoma are two rare myeloid neoplasms. RARS-T is a Myelodysplastic/Myeloproliferative Neoplasm (MDS/MPN) characterized by overlapping myeloproliferative (platelets count higher than 450x109/L associated with proliferation of large atypical megakaryocytes similar than those observed in essential thrombocythemia) and myelodysplastic features (dysplastic erythroid proliferation with ring sideroblasts >15%). RARS-T molecular pattern also exhibited myelodysplastic and myeloproliferative overlap with frequent SF3B1 and JAK2 mutations, justifying its classification in MDS/MPN disorders. Granulocytic Sarcoma also referred as myeloid sarcoma or chloroma are rare extramedullary tumors of immature myeloid cells that partially or totally efface the tissue architecture. Extramedullary involvements include a large variety of clinical significant phenomena that often pose diagnosis problems. Granulocytic sarcoma may develop de novo or concurrently with acute myeloid leukemia or myeloproliferative neoplasms. However, no previous case of granulocytic sarcoma associated to myelodysplastic/myeloproliferative neoplasms has been reported. Herein, we report a case of RARS-T revealed by an asymptomatic thrombocytosis complicated by a granulocytic sarcoma ten months after initial diagnosis. This extramedullary megakaryoblastic mass invaded the sternum and the parietal soft tissues without associated myeloid leukemia.