Characterization of cryptic rearrangements, deletion, complex variants of PML, RARA in acute promyelocytic leukemia

Abstract

Acute promyelocytic leukemia (APL) is characterized by a reciprocal translocation t(15;17)(q22;q21) leading to the disruption of Promyelocytic leukemia (PML) and Retionic Acid Receptor Alpha (RARA) followed by reciprocal PML–RARA fusion in 90% of the cases. Fluorescence in situ hybridization (FISH) has overcome the hurdles of unavailability of abnormal and/or lack of metaphase cells, and detection of cryptic, submicroscopic rearrangements. In the present study, besides diagnostic approach we sought to analyze these cases for identification and characterization of cryptic rearrangements, deletion variants and unknown RARA translocation variants by application of D-FISH and RARA break-apart probe strategy on interphase and metaphase cells in a large series of 200 cases of APL. Forty cases (20%) had atypical PML–RARA and/or RARA variants. D-FISH with PML/RARA probe helped identification of RARA insertion to PML. By application of D-FISH on metaphase cells, we documented that translocation of 15 to 17 leads to 17q deletion which results in loss of reciprocal fusion and/or residual RARA on der(17). Among the complex variants of t(15;17), PML–RARA fusion followed by residual RARA insertion closed to PML–RARA on der(15) was unique and unusual. FISH with break-apart RARA probe on metaphase cells was found to be a very efficient strategy to detect unknown RARA variant translocations like t(11;17)(q23;q21), t(11;17)(q13;q21) and t(2;17)(p21;q21). These findings proved that D-FISH and break-apart probe strategy has potential to detect primary as well as secondary additional aberrations of PML, RARA and other additional loci. The long-term clinical follow-up is essential to evaluate the clinical importance of these findings.

Typical, atypical and cryptic t(15;17)(q24;q21) (PML::RARA) observed in acute promyelocytic leukemia: A retrospective review of 831 patients with concurrent chromosome and PML::RARA dual‐color dual‐fusion FISH studies

“…9 Another subset of 14 (2%) cases was characterized by a primary clone with an isoderivative chromosome 17q which has previously been suggested to arise from duplication of the der(17q) with consequent overrepresentation of the reciprocal RARA::PML fusion and loss of 17p including the tumor suppressor gene TP53 with a resulting deleterious prognostic effect. 21 Of note, Group C had an additional 16,22 In 3% of cases, an additional fusion signal was documented, mostly from a concurrent clone with an isoderivative chromosome 17q.…”

“…A single fusion signal with or without concurrent balanced or unbalanced separate red and green signals, indicating loss or alteration of the reciprocal RARA::PML fusion event, was observed in half of these cases (3%). These may arise from submicroscopic deletions encompassing the reciprocal RARA::PML fusion event on the derivative chromosome 17 (1R1G1F‐type pattern), loss of material on the long arm of derivative chromosome 17 with retention of PML (2R1G1F‐type pattern) or loss of material on the long arm of the derivative chromosome 17 with retention of RARA (1R2G1F‐type pattern) 16,22 . In 3% of cases, an additional fusion signal was documented, mostly from a concurrent clone with an isoderivative chromosome 17q.…”

“…However, atypical genetic mechanisms leading to uncharacteristic findings on genetic investigation such as complex translocations, insertions of RARA into PML or PML into RARA also occur. 8 Although atypical genetic results associated with an APL diagnosis have been described in single and small case series, [9][10][11][12][13][14][15][16] a study capturing the breadth of results in newly diagnosed APL investigated with concurrent chromosome and PML::RARA D-FISH analysis has yet to be comprehensively described. Herein, we provide the largest-scale portrait of concurrent conventional chromosome and PML::RARA D-FISH results obtained from diagnostic APL specimens over 18.5 years from a large referral cytogenetic laboratory.…”

Impact of additional genetic abnormalities at diagnosis of chronic myeloid leukemia for first-line imatinib-treated patients receiving proactive treatment intervention

“…44 The Phassociated rearrangements emphasize that the formation of the BCR::ABL1 gene fusion in some patients may result from a multi-step process. 45,46 Similar rearrangements have been identified in other fusion-based hematological malignancies, such as acute promyelocytic leukemia, 47,48 characterized by the PML::RARA fusion, and RUNX1::RUNXT1 mutated acute myeloid leukemia, 49,50 a sub-type generally associated with a favorable prognosis. In both contexts, these genomic findings have been associated with poor outcomes.…”

Chromosomal aberrations in hematological malignancies: A guide to the identification of novel oncogenes

“…In this issue, Amare et al . [ 2 ] studied a large group of patients with acute promyelocytic leukemia (APL), which results from a reciprocal translocation t(15; 17)(q 22; q21), molecularly PML-RARA fusion gene. The authors highlighted variant translocations, insertions and deletions of RARA gene in APL patients using D-FISH.…”