Abstract
The aim of this study was to review the histopathological, phenotypic, and molecular characteristics of pediatric-type follicular lymphoma (PTFL) and to assess the diagnostic value of novel immunohistochemical markers in distinguishing PTFL from follicular hyperplasia (FH). A total of 13 nodal PTFLs were investigated using immunohistochemistry, fluorescence in situ hybridization (FISH), and PCR and were compared with a further 20 reactive lymph nodes showing FH. Morphologically, PTFL cases exhibited a follicular growth pattern with irregular lymphoid follicles in which the germinal centers were composed of numerous blastoid cells showing a starry-sky appearance. Immunohistochemistry highlighted preserved CD10 (13/13) and BCL6 (13/13) staining, CD20 (13/13) positivity, a K light chain predominance (7/13), and partial BCL2 expression in 6/13 cases (using antibodies 124, E17, and SP66). The germinal center (GC)–associated markers stathmin and LLT-1 were positive in most of the cases (12/13 and 12/13, respectively). Interestingly, FOXP-1 was uniformly positive in PTFL (12/13 cases) in contrast to reactive GCs in FH, where only a few isolated positive cells were observed. FISH revealed no evidence of BCL2, BCL6, or MYC rearrangements in the examined cases. By PCR, clonal immunoglobulin gene rearrangements were detected in 100% of the tested PTFL cases. Our study confirmed the unique morphological and immunophenotypic features of PTFL and suggests that FOXP-1 can represent a novel useful diagnostic marker in the differential diagnosis between PTFL and FH.
Highlights
Pediatric-type follicular lymphoma (PTFL) is a distinct clinicopathological entity in the revised 4th edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues [1]. PTFL was initially identified in pediatric patients, accounting for approximately 1–2% of all pediatric non-Hodgkin lymphomas (NHL), it was subsequently found to occur in young adults and more rarely in older patients [1,2,3,4,5,6,7,8,9,10,11,12]
Pathological, and immunophenotypic review, the 24 excluded cases comprised 6 inadequate samples, 8 cases re-classified as pediatric-type marginal zone lymphoma, 5 cases recognized as conventional FL, and 2 cases with extranodal localization involving the testis and conjunctiva
PTFL is an uncommon clinicopathological entity newly recognized in the revised 4th edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues
Summary
Pediatric-type follicular lymphoma (PTFL) is a distinct clinicopathological entity in the revised 4th edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues [1]. PTFL was initially identified in pediatric patients, accounting for approximately 1–2% of all pediatric non-Hodgkin lymphomas (NHL), it was subsequently found to occur in young adults and more rarely in older patients [1,2,3,4,5,6,7,8,9,10,11,12]. Because of differences in histopathologic features, molecular profile, and clinical behavior, the revised 4th edition of WHO classification excluded from this category extranodal follicular lymphoma (FL) cases involving testis, epididymis, gastrointestinal tract, and kidney, which had been previously reported as PTFL [1]. Another entity that should be excluded is the new provisional entity Blarge B-cell lymphoma (LBCL) with IRF4 rearrangement,^ [1, 13,14,15] which usually presents in Waldeyer’s ring and/or cervical lymph nodes but can arise in the gastrointestinal tract; this lesion may be exclusively follicular, follicular and diffuse, or diffuse
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