An atypical promyelocytic sarcoma and pleural effusion in a patient with Gorham's disease: Efficiency of ATRA/ATO‐based treatment

KEY CLINICAL MESSAGE: This is the first case of a promyelocytic sarcoma diagnosed on pleural effusion and exposed the difficulty of demonstrating a leukemic phase in patients with bone diseases, such as Gorham's disease. It also showed that promyelocytic sarcoma can be treated by ATRA/ATO‐based therapy with an efficient and tolerated response. ABSTRACT: Myeloid sarcoma (MS) is a rare extramedullary tumoral infiltration of immature myeloid cells and can occur in different sites of the body, without leukemic infiltration. A 38‐year‐old woman patient presented at emergency with a pleural effusion, bicytopenias, and Gorham's disease, a very rare bone disorder. In the following days, she worsened with a chylothorax and pancytopenias. Pleural puncture cytologically revealed promyelocytes with Auer rods. Cytogenetic and molecular analyses subsequently confirmed the presence of the t(15:17) translocation. However, no circulating phase of these atypical promyelocytes was found. Similarly, no other origin was identified. We conclude that the patient had a MS of unknown etiology in the form of a pleural effusion with pathological promyelocytes. The patient was treated with a combination of oral all‐trans retinoic acid (ATRA) and arsenic trioxide (ATO) with a cytological and molecular remission persisting 3 months after diagnosis. We report here the first case of a promyelocytic MS of pleural origin without concomitant evidence of acute promyelocytic leukemia. We also show the efficacy of ATRA/ATO treatment in this etiology.