Clinicopathological and molecular characteristics of pediatric type follicular lymphoma

Abstract

Pediatric follicular lymphoma (PTFL) is one of the rare pediatric-type indolent B-cell lymphomas that clinicopathologically differs from adult lymphoma. Accurate diagnosis of PTFL is essential to avoid leak-diagnosis, misdiagnosis and overtreatment, but it is often challenging. To improve the understanding of PTFL, we collected four cases of PTFL, and analyzed the clinicopathological features, differential diagnosis and molecular mutation characteristics of PTFL by hematoxylin‑eosin stain, immunohistochemistry, polymerase chain reaction (PCR), fluorescence in situ hybridization (FISH) and Next Generation Sequencing (NGS). The relevant literature review was also performed. Four PTFL patients were all male, aged 6, 18, 13 and 15 years, and St. Jude were staged III. and I.. Microscopic results showed that the lymph node structure was destroyed; the tumor follicles were enlarged and irregular; medium-large blast-like cells with a consistent shape were visible in tumor follicles, and the nucleus was round or oval; the “starry sky” phenomenon was easy to discover. Tumor cells expressed CD20, PAX-5, Bcl-6, CD10. None of the tumor cells expressed Bcl-2, CD3, CD5, MUM-1, and CyclinD1. CD21 showed dilated growth of follicular dendritic cell (FDC) mesh in tumor follicles. EBER were all negative. FISH testing also showed negative Bcl-2 gene breaks in four cases. A total of 12 related mutant genes including KMT2D, CD79B, GNA13, MYD88, PCLO, TCF3, IRF8, MAP2K1, FOXO1, POLE, INPP5D and FAT4 were detected by NGS. Two of the four cases had IRF8 gene mutation, and one case detected a dual mutation of the MAP2K1 gene. Our data reviewed the unique clinicopathological features and molecular mutational characteristics of PTFL, consolidated the understanding of PTFL, and identified other rare mutant genes, which may further contribute to the study of the molecular mechanism and differential diagnosis of PTFL.