Acute promyelocytic leukemia (APL) is characterized by the promyelocytic leukemia-retinoic acid receptor a (PML-RARA) fusion. In rare instances, RARA is fused to other partners, which dictate sensitivity to targeted therapies. Chen et al previously reported in Blood a novel TBLR1-RARA fusion, which is all-trans-retinoic acid (ATRA)-insensitive in vivo, in a t(3;17)(q26;q21)-harboring APL. 1,2 Here, we report another new RARA fusion resulting from the same translocation in a variant APL patient.The patient was a 36-year-old man who presented with fatigue, dyspnea, and easy bruising for 2 weeks. Complete blood count revealed a hemoglobin level of 5.4 g/dL, platelet count of 41 3 10 9 /L, and white blood cell count of 3.6 3 10 9 /L with 60% hypergranular blasts. Clotting profile showed a decreased fibrinogen level and prolonged prothrombin time but normal activated partial thromboplastin time. Bone marrow (BM) examination showed 68% of blasts with morphology similar to those in peripheral smear ( Figure 1A). The blasts were positive for myeloperoxidase, CD13, CD15, CD33, and CD117 but negative for CD34 and HLA-DR by flow cytometry. A diagnosis of APL was suggested and ATRA (45 mg/m 2 per day) was initiated while awaiting molecular findings. On day 4 of ATRA therapy, the patient developed differentiation syndrome (DS) with fluid retention and pleural effusions. Steroids and diuretics were started, and the 7 1 3 induction chemotherapy was commenced with cytarabine (200 mg/m 2 ) and daunorubicin (60 mg/m 2 ). A morphological complete remission was confirmed at day 30. Figure 1B-C) but the expected TBLR1-RARA fusion previously identified in t(3;17) was absent. No mutations in FLT3, NPM1, CEBPA, DNMT3A, RUNX1, K/NRAS, WT1, or IDH1/2 were detected. Using 59-rapid amplification of complementary DNA ends, we found that RARA was fused to another 3q26 gene called fibronectin type III (FN3) domain containing 3B (FNDC3B) in our patient. Subsequent RT-PCR confirmed the fusion between exon 24 of FNDC3B and exon 3 of RARA ( Figure 1D), which is involved in all other RARA fusions. FNDC3B was originally identified as an adipocyte differentiation factor.3 It contains 9 FN3 domains, which are implicated in protein interactions. The full-length FNDC3B-RARA transcript is predicted to encode a 1461-amino acid protein, containing 8 FN3 domains of FNDC3B as well as the DNA-binding and ligand-binding domain of RARA ( Figure 1E). Two reciprocal RARA-FNDC3B transcripts were also detected. The major transcript involves an in-frame fusion between RARA exon 2 and FNDC3B exon 25, whereas the minor transcript involves an out-offrame fusion between the same RARA exon and FNDC3B exon 26 ( Figure 1D). These transcripts are expected to generate 205-and 111-amino acid proteins, respectively ( Figure 1E). Both FNDC3B-RARA and RARA-FNDC3B fusions were undetected after the patient