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Case Reports
. 2016 Jul;44(7):603-13.
doi: 10.1016/j.exphem.2016.04.011. Epub 2016 May 13.

Comprehensive Genomic Analysis Reveals FLT3 Activation and a Therapeutic Strategy for a Patient With Relapsed Adult B-lymphoblastic Leukemia

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Case Reports

Comprehensive Genomic Analysis Reveals FLT3 Activation and a Therapeutic Strategy for a Patient With Relapsed Adult B-lymphoblastic Leukemia

Malachi Griffith et al. Exp Hematol. .
Free PMC article

Abstract

The genomic events responsible for the pathogenesis of relapsed adult B-lymphoblastic leukemia (B-ALL) are not yet clear. We performed integrative analysis of whole-genome, whole-exome, custom capture, whole-transcriptome (RNA-seq), and locus-specific genomic assays across nine time points from a patient with primary de novo B-ALL. Comprehensive genome and transcriptome characterization revealed a dramatic tumor evolution during progression, yielding a tumor with complex clonal architecture at second relapse. We observed and validated point mutations in EP300 and NF1, a highly expressed EP300-ZNF384 gene fusion, a microdeletion in IKZF1, a focal deletion affecting SETD2, and large deletions affecting RB1, PAX5, NF1, and ETV6. Although the genome analysis revealed events of potential biological relevance, no clinically actionable treatment options were evident at the time of the second relapse. However, transcriptome analysis identified aberrant overexpression of the targetable protein kinase encoded by the FLT3 gene. Although the patient had refractory disease after salvage therapy for the second relapse, treatment with the FLT3 inhibitor sunitinib rapidly induced a near complete molecular response, permitting the patient to proceed to a matched-unrelated donor stem cell transplantation. The patient remains in complete remission more than 4 years later. Analysis of this patient's relapse genome revealed an unexpected, actionable therapeutic target that led to a specific therapy associated with a rapid clinical response. For some patients with relapsed or refractory cancers, this approach may indicate a novel therapeutic intervention that could alter outcome.

Figures

Figure 1
Figure 1. Study overview
(A) Timeline depicting sample collection during the course of disease treatment and progression. Each sample profiled by one of five approaches is indicated as a box placed along a timeline representing the patient’s disease course. Time points are indicated in days with day 0 representing the day of B-ALL diagnosis. Coloring of each box depicts the type of molecular profiling applied to that sample. Tissue details are encoded in the abbreviated sample names. Use of ‘A’ or ‘I’ in sample names indicates expected disease status (Active or Inactive). The most comprehensively profiled sample used for much of the mutation discovery described in this work was ‘SB_d3072_A’, a sorted blast sample (CD45−/CD19+/CD34+) obtained from marrow at the time of second relapse on day 3,072. At the time of publication the patient had achieved a complete response and has been disease free for ~4 years. For additional details on each sample and data type generated, refer to Table S1. (B) Overview of the integrated analysis approach used in this case along with simplified depictions of key analysis activities.
Figure 2
Figure 2. An overview of genomic findings in the second relapse
Circos plot of the somatic events identified in the second relapse. The outermost ring displays an ideogram highlighting genes outlined in Table 1. The first data track identifies single nucleotide variants (black) and small insertions (red) and deletions (blue). The next innermost track displays copy number gains (red) and losses (blue) relative to the normal sample. Deletions targeted for FISH analysis are indicated with an asterisk (*). The innermost track displays loss of heterozygosity as the change in variant allele frequency from normal to tumor cells at germline heterozygous sites. The center of the ring displays structural variants identified in the DNA from two algorithms (Breakdancer = black, Manta = red).
Figure 3
Figure 3. Transcriptome analysis of second relapse reveals aberrant expression of FLT3
(A) Analysis of the ALL1 transcriptome compared to sorted blood cells from 18 healthy individuals (Methods) revealed FLT3 as an important and clinically actionable target. (B) Evaluation of the expression levels of FLT3 in ALL1 versus the healthy control-derived blood cells reflects a difference of several orders of magnitude. (C) FLT3 expression is an outlier across all expressed genes in ALL1, a statistical anomaly otherwise observed only in hematopoietic progenitor (CD34+) cells, and at a magnitude several times higher than in those cells. Legend for control samples: CD14+ (monocytes), CD19+ (B-cells; CD33−/CD19+), CD3+ (T-cells; CD33−/CD3+), CD34+ (hematopoietic progenitors), PMN (neutrophils; CD33−/CD15+/CD16+), and Pro (promyelocytes; CD14−/CD15+/CD16low/−). (D) Microarray evaluation of ALL1 and 207 childhood B-ALL samples reveals that FLT3 is more highly expressed in ALL1 than in any other B-ALL sample in the pediatric study. The three red points shown for ALL1 represent technical replicates run on the same microarray expression platform as the 207 B-ALLs (Affymetrix Human Genome U133 Plus 2.0 Array, Methods).
Figure 4
Figure 4. Personalized genomic assays for assessment of tumor burden and response to treatment
Disease burden and evidence for disease clearance prior to the final MUD allograft were assessed by three orthogonal approaches: VAFs from deep custom capture sequencing for validated somatic SNVs, quantitative FISH for four somatic large-scale deletions, and qPCR of a somatic EP300-ZNF384 translocation breakpoint found to be a possible early/initiating event in this tumor. Time points assayed range from the day of initial diagnosis (day 0) to the patient’s most recent follow-up biopsy obtained ~2.5 years into his current sustained remission (day 4,024). (A) VAFs of 1,588 somatic variants are displayed for eight samples across six time points from diagnosis of the primary B-ALL (day 0), first relapse (day 1,893), and second relapse (day 3,068/3,072). A 40× coverage filter was applied to the primary samples further limiting variants to approximately 581 and 270 for the slide and clot, respectively (Methods). (B) Results from quantitative FISH (Methods) are displayed for four structural deletions utilized to assess tumor burden at the second relapse and following weeks. Refer to Table S3 for details on each deletion assayed. Key treatment time points are indicated with black arrows. (C) VAFs of somatic variants used to assess disease clearance at day 3,219 and day 4,024 are contrasted with their VAFs during refractory disease post salvage therapy (day 3,107) and in the normal skin sample obtained during the first remission (day 42). The sample from day 3,137 was obtained 13 days after initiation of sunitinib, and demonstrates a highly significant reduction in average VAFs compared to that of day 3,107 (p-value < 2.2e-16; n=1,588; Wilcox signed-rank test). (D) qPCR data representing abundance (2ΔΔCT) of the EP300-ZNF384 breakpoint in genomic DNA is displayed for a dilution series of the day 3,072 relapse sample with an unrelated skin sample (grey), six disease samples designated by the day of collection, three samples obtained after the MUD transplant, a matched skin normal obtained in first remission (day 42), and a skin sample from an unrelated donor who did not have this translocation (used as a reference to measure assay “noise”) Note the non-linear, square root transformed values used for display purposes (Methods).

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