Acute promyelocytic leukemia presented as a relapse of acute myeloid leukemia
Authors: Candida Vitale, Elias Jabbour, Xinyan Lu, Mariko Yabe, Rashmi Kanagal Shamanna, Naval Daver, Naveen Pemmaraju, Carlos E. Bueso‐Ramos, Koichi Takahashi
Journal: American Journal of Hematology (2016)

To the Editor: In July 2014, a 42-year-old woman presented with complaints of generalized fatigue, easy bruising, and hematuria. She was found to have leukocytosis with increased myeloblasts (91%). Morphological and immunophenotypic findings were consistent with acute myeloid leukemia (AML) (Fig. 1A). Cytogenetic analysis of the peripheral blood showed a del(6q) abnormality (Fig. 2A), fluorescence in situ hybridization (FISH) did not show the PML-RARA fusion, and targeted gene sequencing revealed a FLT3-internal tandem duplication (ITD) mutation with a 24 base pair (bp) insertion. NPM1, IDH1, IDH2, ASXL1, TET2, DNMT3A, and KIT were tested wild type (WT). The patient was treated with induction chemotherapy consisting of idarubicin and cytarabine and achieved a complete remission. She then received three cycles of high-dose cytarabine as consolidation therapy. However, in January 2015, approximately 6 months after diagnosis, she was found to have leukemia relapse and was referred to our institution for further treatment. Morphology, immunohistochemistry, and immunofluorescence assessments. A: Peripheral blood smear at the time of original AML diagnosis (Wright–Giemsa stain, 1,000×). B: Bone marrow core biopsy specimen at relapse shows 90–100% cellularity (hematoxylin and eosin, 100×). C: High-magnification view of bone marrow specimen at relapse shows a marrow space largely replaced by sheets of immature mononuclear cells with irregular nuclear contours and moderate amounts of cytoplasm (hematoxylin and eosin, 400×). D, E: Bone marrow aspirate smears at relapse show an increased blast population with nuclear folding and scant to moderate amounts of cytoplasm without Auer rods, sharing similar features with the blasts from the initial diagnosis. Myeloperoxidase staining is positive (D: Wright–Giemsa stain, 1000×; E: Myeloperoxidase stain, 1,000×). F: Immunofluorescent staining with promyelocytic oncogenic domain (POD) antibody in relapsed bone marrow sample shows microgranular pattern (POD fluorescence stain, 1000×). Conventional cytogenetic and PML-RARA FISH studies. A: Cytogenetic analysis of peripheral blood sample at original diagnosis shows del(6q) in 2 of 30 cells and no aberrations involving chromosomes 15 and 17. B: Cytogenetic analysis of bone marrow sample at relapse shows inv(3)(q12q27), add(22)(p11·2), and no apparent aberrations involving chromosomes 15 and 17. C: Interphase dual color dual fusion FISH on bone marrow sample at relapse shows one fusion signal with two red (PML) and one green (RARA) signals in 98.5% of the cells. D: Metaphase FISH on bone marrow sample at relapse reveals a red (PML) signal on two normal chromosome 15, a green (RARA) signal on one normal chromosome 17, and a fusion signal on the abnormal chromosome 17, confirming a cryptic ins(17;15)(q21;q24q24). E: Interphase FISH on peripheral blood sample from initial diagnosis confirms the absence of a PML-RARA rearrangement in 500 cells. On presentation to our institution, she had leukocytosis with 91% myeloblasts and disseminated intravascular coagulation (DIC) with low fibrinogen and mildly prolonged prothrombin time. She complained of persistent severe headaches and was found to have intracranial hemorrhage requiring neurosurgical intervention. A bone marrow biopsy specimen showed hypercellular marrow with increased myeloblasts (Fig. 1B–E). Morphological examination of blasts was similar to the original AML (Fig. 1B). Cytogenetic analysis showed inv(3)(q12q27) and add(22)(p11·2) abnormalities; del(6q) was not detected (Fig. 2B). Targeted gene sequencing revealed the same FLT3-ITD mutation with 24 bp insertion, findings consistent with relapsed AML. Again, NPM1, IDH1, IDH2, ASXL1, TET2, DNMT3A, and KIT were tested WT. Salvage therapy with fludarabine, cytarabine, and sorafenib was started. Seven days after presentation, the results of nanofluidics-based qualitative multiparametric reverse-transcriptase polymerase chain reaction (PCR) assay came back as positive for a short form of the PML-RARA fusion transcript. The presence of the PML-RARA fusion transcript was also confirmed by promyelocytic oncogenic domain testing (Fig. 1F) 1 and by quantitative real-time PCR. These results led to the diagnosis of acute promyelocytic leukemia (APL). Treatment with all-trans-retinoic acid (ATRA) and idarubicin was started immediately, but despite these efforts she died the following day of progressive multiple organ failure with DIC. Given the unexpected presentation, we further investigated the biologic and molecular characteristics of her disease. In the bone marrow aspiration sample in which relapse was diagnosed, FISH confirmed a cryptic PML-RARA nuclear fusion signal in 99% of the cells (Fig. 2C). We used the LSI PML-RARA Dual Color, Dual Fusion Translocation Probe (Abbott, Park, IL). This finding was correlated with the results of routine cytogenetics, mapping back to three previously G-banded metaphases, and confirmed the presence of a cryptic ins(17;15)(q21;q24q24) (Fig. 2D). We questioned whether the cryptic PML-RARA fusion had been missed in the original AML sample, which did not show a PML-RARA fusion initially. Therefore, we tested the original AML sample with the same FISH probe that was used in the relapse sample. However, no such PML-RARA fusion was detected in the original AML sample even after assessment of 500 cells (Fig. 2E). Based on these findings, we inferred a model of clonal evolution in this case that the original AML clone carrying FLT3-ITD later acquired the PML-RARA fusion as a secondary event, contributing to relapse of the disease as APL. The PML-RARA fusion protein is a hallmark of APL, and the fusion is generally considered a founding event in leukemogenesis 2. To our knowledge, secondary acquisition of PML-RARA in relapsed AML has not been described. It is still possible that there was a subclonal PML-RARA that was under the detectable threshold and the PML-RARA subclone underwent clonal selection during initial chemotherapy and contributed to the relapse. Another possibility is a therapy-related APL (t-APL), which has been described in patients who were treated with anthracycline chemotherapy. The current case is unlikely to be t-APL because cryptic insertion is not a typical abnormality associated with t-APL 3, 4. Furthermore, our patient received only one cycle of idarubicin for her AML, and only 6 months elapsed between the diagnoses of AML and APL; both would conflict with a diagnosis of t-APL. Since the clinical presentation of this patient was consistent with relapsed AML, we did not expect the patient to have APL. Morphological similarity of blast cells and the presence of the same FLT3-ITD in both original and relapsed leukemia samples made difficult for us to suspect APL. In retrospect, the patient's presentation of intracranial hemorrhage and DIC at relapse is consistent with APL presentation. The prompt detection of PML-RARA has profound therapeutic implications, as nearly all patients with APL respond to ATRA and delay in ATRA administration has been shown to be associated with early death in some studies 5. Like in the current case, morphology and cytogenetics may not be sufficient to rule out the presence of the PML-RARA fusion. In such cases, non-biased screening methods such as nanofluidics-based multiparametric qualitative PCR for leukemia-related fusion transcripts can be helpful. Although the current case represents a rare scenario, it reminds us again how it is crucial to screen for the PML-RARA fusion in virtually all myeloid leukemia cases, even in the relapse setting. Candida Vitale,1 Elias Jabbour,1 Xinyan Lu,2 Mariko Yabe,2 Rashmi Kanagal Shamanna,2 Naval Daver,1 Naveen Pemmaraju,1 Carlos E. Bueso-ramos,2 And Koichi Takahashi1* 1Department of Leukemia, the University of Texas MD Anderson Cancer Center, Houston, Texas; 2Department of Hematopathology, the University of Texas MD Anderson Cancer Center, Houston, Texas