Longitudinal Molecular Characterization of a Rare TPM3::PDGFRB-Rearranged Myeloid/Lymphoid Neoplasm With Late CNL-Like Neutrophilic Evolution.
Frédéric Lambert, Benjamin Koopmansch, Rafael Fernandez Carazo et al.
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Case in brief
An elderly patient presented with hypereosinophilia and a balanced t(1;5)(q21;q33), with PDGFRB rearrangement detected in 70% of nuclei. RNA sequencing identified an in-frame TPM3 exon 8–PDGFRB exon 11 fusion, confirmed by optical genome mapping. Low-dose imatinib produced durable haematologic and cytogenetic remission of the fusion-driven eosinophilic component. Later, the patient developed a CNL-like neutrophilic phase with additional or expanded myeloid mutations, but without re-emergence of the PDGFRB rearrangement; the clonal relationship between the phases remained unresolved.
What made this case unusual
The case combined a rare TPM3::PDGFRB fusion with a late CNL-like neutrophilic phase after durable suppression of the fusion-positive eosinophilic component. The neutrophilic progression occurred without detectable re-emergence of the PDGFRB rearrangement.
Diagnostic / clinical pearl
In a PDGFRB-rearranged neoplasm, assess evolving blood-count and morphologic changes with longitudinal fusion testing alongside myeloid mutational profiling; a later neutrophilic phase may occur without detectable PDGFRB rearrangement.
Why it matters
The clonal relationship between the fusion-driven eosinophilic disease and later neutrophilic progression was unresolved, underscoring the complexity of interpreting disease evolution in this case.