We conducted a retrospective population-based study of patients diagnosed with acute myeloid leukemia (AML) in northern England (population 3.1 million) in order to assess the impact of age and ...genetics on outcome. Four hundred and sixteen patients were diagnosed with AML, between 2007 and 2011. In those aged ≤60 years (n = 20) with acute promyelocytic leukemia (APL) overall survival (OS) was 100%. For non-APL patients aged ≤60 years, OS for those with favorable, intermediate and adverse cytogenetics was not reached, 17 and 9.8 months, respectively (p = 0.0001). Of particular note, intensively treated patients aged >60 years with intermediate cytogenetics and FLT3−/NPM1+ status had a five-year survival of 60% versus median OS of 11 months for other subsets (p = 0.04). Population-based studies reduce selection bias and have utility in studying rarer diseases, particularly in populations that recruit poorly to trials. The highly favorable outcome in our subgroup of intensively-treated FLT3−/NPM1+ older patients merits further study.
Fusion genes derived from the platelet-derived growth factor receptor beta (PDGFRB) or alpha (PDGFRA) play an important role in the pathogenesis of BCR-ABL–negative chronic myeloproliferative ...disorders (CMPDs). These fusion genes encode constitutively activated receptor tyrosine kinases that can be inhibited by imatinib. Twelve patients with BCR-ABL–negative CMPDs and reciprocal translocations involving PDGFRB received imatinib for a median of 47 months (range, 0.1-60 months). Eleven had prompt responses with normalization of peripheral-blood cell counts and disappearance of eosinophilia; 10 had complete resolution of cytogenetic abnormalities and decrease or disappearance of fusion transcripts as measured by reverse transcriptase–polymerase chain reaction (RT-PCR). Updates were sought from 8 further patients previously described in the literature; prompt responses were described in 7 and persist in 6. Our data show that durable hematologic and cytogenetic responses are achieved with imatinib in patients with PDGFRB fusion–positive, BCR-ABL–negative CMPDs.
The BCR–ABL‐negative chronic myeloproliferative disorders (CMPD) and myelodysplastic/myeloproliferative diseases (MDS/MPD) are a spectrum of related conditions for which the molecular pathogenesis is ...poorly understood. Translocations that disrupt and constitutively activate the platelet‐derived growth factor receptor β(PDGFRB) gene at chromosome band 5q33 have been described in some patients, the most common being the t(5;12)(q33;p13). An accurate molecular diagnosis of PDGFRB‐rearranged patients has become increasingly important since recent data have indicated that they respond very well to imatinib mesylate therapy. In this study, we have tested nine patients with a CMPD or MDS/MPD and a translocation involving 5q31–33 for disruption of PDGFRB by two‐colour fluorescence in situ hybridization (FISH) using differentially labelled, closely flanking probes. Normal control interphase cells gave a false positive rate of 3% (signals more than one signal width apart). Six patients showed a pattern of one fused signal (from the normal allele) and one pair of signals separated by more than one signal width in > 85% of interphase cells, indicating that PDGFRB was disrupted. These individuals had a t(1;5)(q21;q33), t(1;5)(q22;q31), t(1;3;5)(p36;p21;q33), t(2;12;5)(q37;q22;q33), t(3;5) (p21;q31) and t(5;14)(q33;q24) respectively. The remaining three patients with a t(1;5)(q21;q31), t(2;5)(p21;q33) and t(5;6)(q33;q24–25) showed a normal pattern of hybridization, with ≥ 97% interphase cells with two fusion signals. We conclude that two‐colour FISH is useful to determine the presence of a PDGFRB rearrangement, although, as we have shown previously, this technique may not detect subtle complex translocations at this locus. Our data indicate that several PDGFRB partner genes remain to be characterized.
We have identified three patients (2 adults, one infant) who presented with BCR-ABL negative eosinophilic myeloproliferative disorders. Cytogenetic analysis revealed a t(1;3;5)(p36;p21;q33) for case ...1 and a t(3;5)(p21–25;q31–35) for cases 2 and 3. Two-color fluorescence in situ hybridization (FISH) using differentially labelled probes flanking PDGFRB indicated that this gene was disrupted in all three cases. 5′ rapid amplification of cDNA ends (5′RACE) for case 1 identified an in-frame mRNA fusion of exon 9 of the WDR48 gene at 3p21 to exon 12 of PDGFRB. The chimeric mRNA is predicted to encode a 872 amino acid fusion protein that retains the amino terminal WD repeat region of WDR48 fused to the transmembrane and intracellular tyrosine kinase domains of PDGFRbeta. Cases 2 and 3 were negative for the WDR48-PDGFRB fusion mRNA by RT-PCR using several combinations of primers. 5′RACE PCR from case 2 RNA identified a fusion involving a second 3p21 gene: GOLGA4 exon 11 was fused in-frame to exon 11 of PDGFRB. Exactly the same fusion was found in case 3. The predicted 991 amino acid protein included the amino terminal coiled-coil domain of GOLGA4 fused to the transmembrane and intracellular tyrosine kinase domains of PDGFRbeta. Interestingly, both WDR48 and GOLGA4 are involved in endocytic shuttling pathways. The presence of all fusions was confirmed by RT-PCR and identification of the genomic breakpoints. Imatinib, a known inhibitor of PDGFRbeta, selectively blocked the growth of patient CFU-GM for case 2. Following the identification of PDGFRB rearrangements, all three patients were treated with imatinib. Case 1 was in transformation, but responded rapidly to minimal doses of imatinib (800mg daily for 4 days) with complete cytogenetic remission but remained pancytopenic. Blast crisis recurred 8 months later, responded similarly to 3 days of imatinib, but the patient died 2 months later of invasive fungal infection. Case 2 responded clinically and remains in sustained cytogenetic and molecular remission (nested RT-PCR negative for GOLGA4-PDGFRB). Case 3 (a 13 month old boy) had a complete hematologic response to 50mg/day imatinib but the t(3;5) was still seen in 40% of metaphases at 3 months. We conclude that PDGFRB fuses to diverse partner genes to give rise to atypical MPDs. Although very rare, identification of these fusions is critical for proper management of affected individuals.
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