Primary follicular lymphoma of the testis in childhood: An entity with peculiar clinical and molecular characteristics

Background/Aims: Paediatric primary follicular lymphoma of the testis (PPFLT) is exceptional: the few reported cases seem to lack BCL-2 gene rearrangement and/or protein expression. The aim of this study was to characterise a PPFLT arising in a 4 year old boy. Methods: This case was characterised using conventional histological analysis, immunohistochemistry, and a polymerase chain reaction based method for the detection of immunoglobulin V_H chain rearrangements. Results: The neoplasm was staged I^E/A; left orchiectomy and chemotherapy were performed, producing complete remission. Histology showed a predominantly follicular lymphoid infiltrate mainly composed of centroblast-like cells. The phenotype was CD20⁺, CD79a⁺, CD10⁺, bcl-6⁺, B cell specific activating protein⁺, κ light chain⁺, CD30^-/+, interferon regulating factor 4^-/+, c-myc^-/+, λ light chain^-, CD3^-, bcl-2^-, p53^-, cytokeratin^-, and placental alkaline phosphatase^-. Lymphomatous elements were found within a CD21⁺ follicular dendritic cell network and 70% were positive for Ki-67/MIB-1. Molecular analysis revealed monoclonal immunoglobulin heavy chain gene rearrangement and BCL-6 mutations, in the absence of BCL-2 major breakpoint and BCL-2 minor cluster region rearrangements, p53 mutations, and death associated protein kinase gene hypermethylation. Conclusions: These findings suggest a different pathogenesis of PPTFL compared with adult follicular lymphoma and might explain its favourable course in spite of aggressive histology.