A global study for acute myeloid leukemia with RARG rearrangement

Abstract

Acute myeloid leukemia (AML) with retinoic acid receptor γ (RARG) rearrangement has clinical, morphologic, and immunophenotypic features similar to classic acute promyelocytic leukemia. However, AML with RARG rearrangement is insensitive to alltrans retinoic acid (ATRA) and arsenic trioxide (ATO) and carries a poor prognosis. We initiated a global cooperative study to define the clinicopathological features, genomic and transcriptomic landscape, and outcomes of AML with RARG rearrangements collected from 29 study groups/institutions worldwide. Thirty-four patients with AML with RARG rearrangements were identified. Bleeding or ecchymosis was present in 18 (54.5%) patients. Morphology diagnosed as M3 and M3v accounted for 73.5% and 26.5% of the cases, respectively. Immunophenotyping showed the following characteristics: positive for CD33, CD13, and MPO but negative for CD38, CD11b, CD34, and HLA-DR. Cytogenetics showed normal karyotype in 38% and t(11;12) in 26% of patients. The partner genes of RARG were diverse and included CPSF6, NUP98, HNRNPc, HNRNPm, PML, and NPM1. WT1- and NRAS/KRAS-mutations were common comutations. None of the 34 patients responded to ATRA and/or ATO. Death within 45 days from diagnosis occurred in 10 patients (∼29%). At the last follow-up, 23 patients had died, and the estimated 2-year cumulative incidence of relapse, event-free survival, and overall survival were 68.7%, 26.7%, and 33.5%, respectively. Unsupervised hierarchical clustering using RNA sequencing data from 201 patients with AML showed that 81.8% of the RARG fusion samples clustered together, suggesting a new molecular subtype. RARG rearrangement is a novel entity of AML that confers a poor prognosis. This study is registered with the Chinese Clinical Trial Registry (ChiCTR2200055810).

Graphical abstract

Figure 1.

Morphologic and immunophenotypic features of patients with AML with RARG rearrangement. (A) Morphologic features of 8 cases with RARG rearrangement (top and middle) and 4 cases with PML::RARA (bottom). Most blasts had hypergranular cytoplasm (UPNs 11, 15-17, and 31 and APL-1, -2, and -4) or hypogranular cytoplasm (UPNs 10, 14, and 19 and APL-3). Auer rods were also present in some cases (UPNs 10 and 14 and APL-1 and -2). Most blasts harbored an irregular round, oval, or bilobed nucleus that was strongly suggestive of French-American-British classification type M3. (B) Comparison of immunophenotyping features between patients with RARG rearrangement (X::RARG, n = 34) and those with PML::RARA (n = 221). The expression of surface markers was not different between the 2 groups, except for CD38 (0 vs 98.5%; P < .0001) and CD117 (84.4% vs 96.7%; P = .01).

Figure 2.

The genomic and transcriptomic landscape of AML with RARG rearrangement. (A) The frequency of concurrent mutation genes profile identified in 24 patients with RARG rearrangement (left) and in 142 patients APL with PML::RARA fusion (right, for comparison). (B) Unsupervised hierarchical clustering identified unique gene expression pattern of RARG rearrangement (RARG). Patients with AML with PML::RARA (APL) and others without RARG or RARA rearrangement are included as comparison. Columns indicate patients with AML and rows represent gene expression levels for each patient. Genes showing overexpression or underexpression in the heatmap are shown in red or blue, respectively. (C-D) Differentially expressed gene (DEG) comparisons between patients with AML with RARG rearrangement (RARG), PML::RARA (APL) and others without RARG or RARA rearrangement (AML). (C) Volcano plots showing DEGs among the 3 subtypes. Most significant DEGs or interested genes are labeled, and CD38, RARA, and RARG are highlighted. (D) The distribution of expression levels for representative genes shown by violin plots. The x-axis indicates the 3 subtypes, whereas the y-axis represents gene expression level (FPKM) in log scale. Each dot corresponds to 1 sample. The significance levels of difference were determined using the Wilcoxon rank-sum test. FPKM, Fragments per kilobase per million. Myeloid TF, myeloid transcription factor.

Figure 3.

The CIR, EFS, and OS of patients with RARG rearrangements (n = 34). CIR, cumulative incidence of relapse; EFS, event-free survival; OS, overall survival.

Figure 4.

The proposed flowchart for the diagnosis and treatment of patients with AML with RARG rearrangement. FISH, fluorescence in situ hybridization; PCR, polymerase chain reaction.