Fluorescent in situ hybridization (FISH) in bone marrow and peripheral blood of leukemia patients: implications for occupational surveillance

Accurate quantification of chromosomal lesions via short tandem repeat analysis using minimal amounts of DNA

Background

Cytogenetic aberrations such as deletion of chromosome 5q (del(5q)) represent key elements in routine clinical diagnostics of haematological malignancies. Currently established methods such as metaphase cytogenetics, FISH or array-based approaches have limitations due to their dependency on viable cells, high costs or semi-quantitative nature. Importantly, they cannot be used on low abundance DNA. We therefore aimed to establish a robust and quantitative technique that overcomes these shortcomings.

Methods

For precise determination of del(5q) cell fractions, we developed an inexpensive multiplex-PCR assay requiring only nanograms of DNA that simultaneously measures allelic imbalances of 12 independent short tandem repeat markers.

Results

Application of this method to n=1142 samples from n=260 individuals revealed strong intermarker concordance (R²=0.77–0.97) and reproducibility (mean SD: 1.7%). Notably, the assay showed accurate quantification via standard curve assessment (R²>0.99) and high concordance with paired FISH measurements (R²=0.92) even with subnanogram amounts of DNA. Moreover, cytogenetic response was reliably confirmed in del(5q) patients with myelodysplastic syndromes treated with lenalidomide. While the assay demonstrated good diagnostic accuracy in receiver operating characteristic analysis (area under the curve: 0.97), we further observed robust correlation between bone marrow and peripheral blood samples (R²=0.79), suggesting its potential suitability for less-invasive clonal monitoring.

Conclusions

In conclusion, we present an adaptable tool for quantification of chromosomal aberrations, particularly in problematic samples, which should be easily applicable to further tumour entities.

Chromosomal effects of non-alkylating drug exposure in oncology personnel

Therapy-related leukemia has been a recognized sequela of cancer treatment for decades with "signature" abnormalities of chromosomes 5, 7, and 11 observed in treated patients. Risk to oncology personnel handling anti-cancer agents has also been documented by non-specific measures of genotoxicity in blood and urine. Using chromosomal markers applied in clinical practice, we previously demonstrated in oncology workers, a dose-related increase in abnormalities of chromosomes 5 and 7, known to be targets of alkylating agent exposure. In the analysis presented here, we extended that work to also assess damage resulting from non-alkylating drug exposure. Peripheral blood lymphocytes from oncology personnel (N = 63) and non-exposed controls (N = 46) was collected and examined using the fluorescent in situ hybridization technique with probes for targets on chromosomes 5, 7, and 11. Participants recorded drug handling events over a 6 week period. Important co-variates were considered. Examining chromosomal outcomes as a function of drug handling frequency, we employed Poisson Regression to obtain incident rate ratios (IRRs) for selected drug handling frequencies. We found a dose-related increase in the IRR for aberrations in all three chromosomes 5, 7, and 11, reaching statistical significance for chromosome 5, as a function of non-alkylating drug handling. This suggests that the targeting of chromosome 5 is not limited to alkylating agent exposure, as some recent evidence in treated patients has also shown. Thus, the pattern of insult observed in treated patients appears to extend to oncology personnel exposed in the workplace.

Molecular cytogenetic monitoring from CD34+ peripheral blood cells in myelodysplastic syndromes: first results from a prospective multicenter German diagnostic study

The gold standard of cytogenetic analysis in myelodysplastic syndromes (MDS) is conventional chromosome banding (CCB) analysis of bone marrow (BM) metaphases. Most aberrations can also be detected by fluorescence-in situ-hybridization (FISH). For this prospective multicenter German diagnostic study (www.clinicaltrials.gov: #NCT01355913) 360 patients, as yet, were followed up to 3 years by sequential FISH analyses of immunomagnetically enriched CD34+ peripheral blood (PB) cells using comprehensive FISH probe panels, resulting in a total number of 19,516 FISH analyses. We demonstrate that CD34+ PB FISH correlates significantly with CCB analysis and represents a feasible method for a reliable non-invasive cytogenetic monitoring from PB.

Partial Trisomy 9p(p22→pter) from a Maternal Translocation 4q35 and 9p22

We present clinical and cytogenetic data on a 7-year-old female child with partial trisomy for 9p22→9pter as a result of a maternal balanced reciprocal translocation. Her karyotype was ascertained as 46,XX,dec(4)t(4;9)(q35; p22)mat. The father had a normal karyotype, while the mother had an apparently balanced translocation involving chromosomes 4 and 9 [46,XX,t(4;9)(q35;p22)]. This case will be briefly compared with other published cases of a similar translocation.

Chromosome-wide aneuploidy study (CWAS) in workers exposed to an established leukemogen, benzene

Evidence suggests that de novo, therapy-related and benzene-induced acute myeloid leukemias (AML) occur via similar cytogenetic and genetic pathways, several of which involve aneuploidy, the loss or gain of chromosomes. Aneuploidy of specific chromosomes has been detected in benzene-related leukemia patients as well as in healthy benzene-exposed workers, suggesting that aneuploidy precedes and may be a potential mechanism underlying benzene-induced leukemia. Here, we analyzed the peripheral blood lymphocytes of 47 exposed workers and 27 unexposed controls using a novel OctoChrome fluorescence in situ hybridization (FISH) technique that simultaneously detects aneuploidy in all 24 chromosomes. Through this chromosome-wide aneuploidy study (CWAS) approach, we found heterogeneity in the monosomy and trisomy rates of the 22 autosomes when plotted against continuous benzene exposure. In addition, statistically significant, chromosome-specific increases in the rates of monosomy [5, 6, 7, 10, 16 and 19] and trisomy [5, 6, 7, 8, 10, 14, 16, 21 and 22] were found to be dose dependently associated with benzene exposure. Furthermore, significantly higher rates of monosomy and trisomy were observed in a priori defined 'susceptible' chromosome sets compared with all other chromosomes. Together, these findings confirm that benzene exposure is associated with specific chromosomal aneuploidies in hematopoietic cells, which suggests that such aneuploidies may play roles in benzene-induced leukemogenesis.