| Summary: | Abstract Context The detection of low‐level persistent or relapsed B‐cell neoplasms, particularly post‐therapy, can be challenging, often requiring multiple testing modalities. Objective Here we investigate the utility of CD19‐based selection of neoplastic B‐cells (CD19S) as an enrichment strategy to improve the detection rate of cytogenetic abnormalities in post‐therapy samples of B‐cell neoplasms, especially those with low‐level disease. Design In a cohort largely comprised of post‐therapy B‐ALL and CLL samples, we performed fluorescence in situ hybridization (FISH) analysis on CD19‐selected cells (CD19S FISH) in 128 specimens from 88 patients, and on non‐selected cells (NS FISH) in a subset of cases. The FISH findings were compared with the concurrent flow cytometry (FC) results in all samples and molecular analysis in a subset. Results CD19S FISH was able to detect cytogenetic aberrations in 86.0% of post‐therapy samples with evidence of disease as determined by routine or MRD FC, compared to 59.1% of samples by NS FISH. CD19S FISH detected significantly higher percentages of positive cells compared to NS FISH (p < 0.001). Importantly, CD19S FISH enabled the detection of emergent subclones (clonal evolution) associated with poor prognosis. Conclusions CD19S FISH can be useful in daily diagnostic practice. Compared to NS FISH, CD19S FISH is quantitatively and qualitatively superior for the detection of cytogenetic aberrations in B‐cell neoplasms, which are important for risk stratification and optimal management of patients with B‐cell neoplasms, especially in the relapsed setting. Although CD19S FISH has a diagnostic sensitivity inferior to that of MRD FC, the sensitivity of this modality is comparable to routine FC for the evaluation of low‐level disease in the post‐therapy setting. Moreover, CD19S samples are invaluable for additional molecular and genetic analyses.
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