[Therapy-related acute promyelocytic leukemia with complex karyotype accompanied by cryptic PML/RARA on chromosome 15 by metaphase FISH].

A 53-year-old male presented with pancytopenia for 13 months. He had a past history of follicular lymphoma and hypopharyngeal cancer, which was treated via chemotherapy and radiotherapy. Bone marrow aspiration biopsy of the patient revealed a hypocellular marrow with 32% of hypergranular blasts without Auer bodies. There were also erythroid and megakaryocytic dysplasia in the bone marrow. Although the PML/RARA transcript was detected by fluorescence in situ hybridization (FISH) and reverse transcription polymerase chain reaction (RT-PCR), the G-banding karyotype analysis showed a complex karyotype without t (15;17). The PML/RARA fusion signal was identified on chromosome 15 by metaphase FISH. The patient was diagnosed of therapy-related acute promyelocytic leukemia (t-APL) with cryptic PML/RARA. He successfully attained molecular complete remission with all-trans retinoic acid (ATRA) and two courses of arsenic trioxide (ATO). He was subsequently administered nivolumab without ATRA maintenance therapy because of a progressing metastasis of a hypopharyngeal cancer to the lung. The patient had a relapse of t-APL following nine courses of nivolumab, 8 months after ending consolidation therapy with ATO. Reinduction therapy with ATRA was not effective for the relapsed t-APL that was accompanied by del (5q) and monosomy 7. Little has been previously reported on t-APL with cryptic PML/RARA. Therefore, the clinical course of this patient may provide useful insights about the characteristics of t-APL with cryptic PML/RARA.