[Therapy-related acute promyelocytic leukemia developing during chemotherapy for thymic carcinoma].

A 74-year-old man was admitted to hospital due to suspected acute leukemia. He had a history of thymic carcinoma, which had been treated with carboplatin in combination with either paclitaxel or amrubicin. However, the tumor remained unresponsive to these treatments. Administration of tegafur/gimeracil/oteracil (TS-1) was initiated, which resulted in tumor size reduction and a partial response. However, leukopenia persisted after the last TS-1 treatment, and four years after the initial treatment, increased blast cell counts were found in a blood film . Bone marrow analysis showed blasts with Auer rods, faggot cells, and dysplastic promyelocytes. Flow cytometry was positive for CD13, CD33, CD34, CD117, and myeloperoxidase, but negative for HLA-DR. PML-RARA fluorescence in situ hybridization was positive. Cytogenetic analysis revealed 47,XY,t (15;17) (q22;q21),+21. Thus, therapy-related acute promyelocytic leukemia (tAPL) was diagnosed. The patient achieved and maintained complete remission for more than 20 months by a de novo APL-treatment regimen including all-trans retinoic acid, arsenic trioxide and tamibarotene. Moreover, the thymic carcinoma has remained stable. Although secondary malignancies of thymic carcinoma have been previously reported, therapy-related leukemia, especially tAPL, is very rare.