A Pragmatic First-Line Screening Assay for PDGFR Rearrangements: A Real-World Clinical Validation

Myeloid/lymphoid neoplasms with tyrosine kinase rearrangements (MLN-TK) are rare clonal eosinophilias driven by PDGFRA, PDGFRB and other kinase fusions, highly sensitive to tyrosine kinase inhibitors. Their detection remains challenging, particularly for cryptic PDGFRA rearrangements. We performed a large multicenter real-world validation of the generic quantitative RT-PCR assay (gPDGFR), which detects 3′ PDGFRA/PDGFRB overexpression independently of fusion partner. A total of 231 consecutive patients with hypereosinophilia from 12 French centers were analyzed, and assay robustness was further assessed in an independent heterogeneous cohort of 102 TKI-treated patients. Twenty-two PDGFR-rearranged cases (14 PDGFRA-r, 8 PDGFRB-r) were identified. The assay demonstrated 100% sensitivity and 100% negative predictive value. For PDGFRA, positive predictive value and specificity reached 100%. In contrast, PDGFRB overexpression showed lower specificity due to borderline false-positive cases, underscoring the need for confirmatory testing. In selected patients, longitudinal gPDGFR kinetics paralleled fusion-specific RT-qPCR, supporting its use for molecular follow-up when dedicated assays are unavailable, although it does not provide quantitative measurable residual disease assessment. Overall, gPDGFR represents a robust, partner-independent first-line screening strategy that can be readily integrated into routine diagnostic workflows to enable timely identification of patients eligible for targeted therapy.