Pediatric-Type Follicular Lymphoma With A Prolonged Clinical Course And Unusual Mutational Profile

Abstract Casestudy: Pediatric-type follicular lymphoma is crucial to differentiate from other subtypes of follicular lymphomas since it carries an excellent prognosis and generally does not require radio- or chemotherapy. We present a 22-year-old male with an 8-year history of a left submandibular mass. Interval imaging studies showed no change in the mass size over time and no other sites of involvement. The patient underwent excision of the mass. Histologic sections showed effacement of nodal architecture with expansile follicles composed of medium sized to large lymphoid cells with blastoid features. Follicles showed abundant tingible body macrophages. Polarization was not seen. Neoplastic follicles were positive for CD20, PAX5, BCL6, CD10, and FOXP1, and negative for BCL2. PD1 positive cells were localized peripherally in the follicles. Clonality was confirmed by flow cytometry (kappa restricted CD10 positive B-cells in a polyclonal background) and by IGH PCR analysis (clonal peaks in FR1 and FR2). Molecular genetic testing showed the following mutations: TNFRSF14 W12* (VAF 14.8%), MAP2K1 F53V (5.7%), EZH2 Y646N (6.9%), ARID1A R1461* (7.1%). BCL2 rearrangement was not detected. MAP2K1 and TNFRSF1 are frequently reported in pediatric-type follicular lymphoma, however in the majority of cases they do not occur together. EZH2 mutation does not typically occur in pediatric-type follicular lymphoma, and is more common in classic adult- onset follicular lymphomas. Despite typical morphologic and clinical features, this patient showed a more complex genetic profile and EZH2 mutation, unusual findings in pediatric-type follicular lymphoma. It is conceivable that a higher genetic complexity has been acquired over time and is related to the long duration of the disease.