Molecular and phenotypic diversity of CBL-mutated juvenile myelomonocytic leukemia

Abstract

Mutations in the gene CBL were first identified in adults with various myeloid malignancies. Some patients with juvenile myelomonocytic leukemia (JMML) were also noted to harbor mutations in CBL, but were found to have generally less aggressive disease courses compared to other forms of Ras pathway-mutant JMML. Importantly, and in contrast to most reports in adults, the majority of CBL mutations in JMML patients are germline with acquired uniparental disomy occurring in affected marrow cells. Here, we systematically studied a large cohort of 33 JMML patients with CBL mutations and found this disease to be highly diverse in presentation and overall outcome. Moreover, we discovered somatically-acquired CBL mutations in 15% of pediatric patients who presented with more aggressive disease. Neither clinical features nor methylation profiling were able to distinguish somatic CBL patients from germline CBL patients, highlighting the need for germline testing. Overall, we demonstrate that disease courses are quite heterogeneous even among germline CBL patients. Prospective clinical trials are warranted to find ideal treatment strategies for this diverse cohort of patients.

Figure 1.

Germline and somatic CBL mutations in patients with juvenile myelomonocytic leukemia. Each dot represents one mutation found at the specified codon. The resulting change in amino acid is coded by colors. The stars represent six patients found to have deletions. 4H: four helix bundle; EF: EF-hand like domain; SH2: Src homology 2 domain; L: linker domain; RF: ring finger domain; Pro-rich: proline-rich domain; UBA/LZ: ubiquitin-associated/leucine zipper domain.

Figure 2.

Kaplan-Meier survival curves for CBL-juvenile myelomonocytic leukemia. (A) Overall survival of the whole cohort (n=33). (B) Overall survival of patients who underwent hematopoietic stem cell transplantation (n=15). (C) Overall survival of patients who did not undergo hematopoietic stem cell transplantation (n=17). One patient who was lost to follow-up was not considered in analyses for (B) or (C). HSCT: hematopoietic stem cell transplantation; w/o: without.

Figure 3.

Swimmer plot showing the clinical course of each patient over time. Each bar represents one patient color-coded based on the presence of germline CBL (blue) or somatic-only CBL (orange). Dates of hematopoietic stem cell transplantation (HSCT), relapse, death or resolution of splenomegaly are depicted by symbols. The current ongoing status of the patient is depicted as a color-coded arrow. Therapeutic agents received by the patient (before HSCT if applicable) are shown on the left side with pattern-coded dots. Clinical features (age, hemoglobin F levels and platelet counts at diagnosis are depicted as filled (if true) or empty (if false) boxes. Dashed boxes are used if data were not available. Information on treatment was missing for patients UPN1125, UPN2949 and UPN 2357; patient UPN2949 was lost to follow-up. HbF: hemoglobin F; PLT: platelet count.

Figure 4.

DNA methylation profiles of patients with CBL-mutated juvenile myelomonocytic leukemia. (A) CBL mutant samples profiled by MethylSeq classified according to the international juvenile myelomonocytic leukemia (JMML) consensus signature. (B) DNA methylation groups low, intermediate, and high were defined using an international cohort of JMML samples described by Schönung et al. Each CBL mutant sample was classified into one of the three methylation groups based on minimum distance to the nearest centroid. Heatmaps (A and B) show the b values of 1,386 CpG loci used for methylation classification. LOH: Loss of heterozygosity. Two patients in the low methylation group are not depicted in (A) because their methylation data were generated with an Illumina 450k array.