FIP1L1::PDGFRA Fusion in a Pediatric Patient Presenting With B-Cell Lymphoblastic Leukemia.

Approximately 10% of Ph-Like patients have ABL class gene fusions, which include the FIP1L1::PDGFRA rearrangement. We report a case of a pediatric patient with Ph-like B-lymphoblastic leukemia (B-LL) with a FIP1L1::PDGFRA fusion and their treatment course using a combination of chemotherapy and targeted therapy with imatinib. A 10-year-old female presented with lethargy, palpitations, and fevers. She had pancytopenia, no eosinophilia, and flow cytometry consistent with B-LL. FISH identified a CHIC2 deletion, suggestive of FIP1L1::PDGFRA fusion, confirmed on next-generation RNA sequencing. The patient commenced targeted therapy with imatinib, which she continued until completion of standard chemotherapy per COG AALL1732. She remains in remission 6 months post-completion of therapy. B-ALL with a FIP1L1::PDGFRA fusion is extremely rare, particularly in pediatrics. FIP1L1::PDGFRA rearrangements can be difficult to detect on routine testing and may not always be seen in association with eosinophilia. Identification of FIP1L1::PDGFRA rearrangements is important as they enable treatment with a tyrosine kinase inhibitor, which has significantly improved the overall prognosis for PDGFRA-rearranged neoplasms. Prospective studies assessing imatinib dosage, duration, and long-term safety are warranted in this cohort.