An interphase fluorescence in situ hybridisation assay for the detection of 3q26.2/EVI1 rearrangements in myeloid malignancies.

Chromosome rearrangements involving band 3q26.2 are associated with myeloid malignancies, aberrant expression of the human ecotropic virus integration site-1 (EVI1) gene, an unfavourable prognosis and an aggressive clinical course. The 3q26.2 rearrangements are characteristically heterogeneous and typically difficult to detect in poor quality metaphases. To develop a dual-colour fluorescence in situ hybridisation (FISH) assay for the detection of 3q26.2/EVI1 aberrations, a series of 10 BAC clones corresponding to the EVI1 gene region were systematically evaluated and narrowed down to two probe sets; one probe set encompassed the EVI1 gene extending centromeric, while the second probe set covered the EVI1 gene and extends telomeric. Both probe sets were evaluated on 35 patient samples with cytogenetically defined 3q26.2 rearrangements collected at various treatment time points, the inv(3)(q21q26.2) Kasumi-4 cell line, and 10 known negative samples. The two-probe set strategy identified all samples, despite the vast breakpoint heterogeneity observed. In samples from acute myeloid leukaemia and myelodysplastic syndrome cases, the majority of inversion breakpoints were 3' to EVI1 whereas 3q26.2 translocation breakpoints frequently mapped 5' to EVI1. However, two 3q26.2 translocation samples had breakpoints 3' to EVI1. Most inv(3q) chronic myeloid leukaemia samples showed breakpoints within the EVI1 gene. This study demonstrated that, despite the extensive breakpoint heterogeneity observed with 3q26.2 aberrations, this FISH strategy is effective for the detection of 3q26.2 abnormalities in myeloid malignancies.

Methylthioadenosine phosphorylase gene deletions are frequently detected by fluorescence in situ hybridization in conventional chondrosarcomas.

Chondrosarcomas are the second most common primary malignant tumor of bone. Chemotherapy for conventional chondrosarcomas is generally ineffective. Methylthioadenosine phosphorylase (MTAP) is a ubiquitous enzyme, essential in the salvage pathway of adenine and in methionine synthesis. MTAP-deficient cells are more susceptible than wild-type cells to pharmacologic inhibitors of de novo purine synthesis. Homozygous deletions of MTAP have been reported in hematologic and solid tumor malignancies. Based on these observations, we investigated the frequency of MTAP deletions in conventional, grade II chondrosarcomas by fluorescence in situ hybridization (FISH) analysis: 23 conventional, grade II chondrosarcoma patient samples from the Cleveland Clinic Foundation were analyzed for MTAP deletions. Nuclei were successfully extracted from 14 of 23 samples (61% evaluable) for FISH analysis: 7 of 14 samples (50%) showed either homozygous or hemizygous deletion of the MTAP gene, 6 of 14 (43%) failed to show deletion, and 1 of 14 (7%) was inconclusive. These findings suggest that approximately one-half of conventional, grade II chondrosarcomas may be preferentially sensitive to pharmacologic inhibitors of de novo purine synthesis. The present study led to development by the Intergroup Coalition Against Sarcomas of a phase II trial of pemetrexed, a multitargeted anti-folate, for advanced chondrosarcomas.