Paediatric follicular lymphoma

Paediatric follicular lymphoma (PFL) is a rare variant of follicular lymphoma accounting for approximately 1%–2% of all paediatric non-Hodgkin lymphomas. PFL shows a male predominance with median age of onset varying from 7.5 to 14 years. PFL most commonly occurs in the head and neck region arising in lymph nodes or lymphoid tissue of Waldeyer's ring; extra-nodal localization is uncommon. Although the optimal clinical management remains unclear, most PFLs are low stage (i.e. localized) disease, and the prognosis is excellent with local excision leading to complete remission in the vast majority of the cases. As a rare lymphoid malignancy molecular and immunophenotypic studies on PFL are limited and both pathogenesis and biology are largely unknown. PFL is characterized by enlarged irregular lymphoid follicles showing high grade (grade 3) histological features. The germinal centres of these follicles are composed predominantly of cells showing “blastoid” morphology, with round to oval nuclei and small nucleoli. In most cases the neoplastic germinal centre cells lack both expression of BCL2 protein and the t(14;18) translocation but approximately one third of the cases can show weak expression of BCL-2 protein and a smaller percentage harbour BCL-2 rearrangements. In the clinical setting PFL has to be distinguished from reactive follicular hyperplasia and paediatric nodal marginal zone lymphoma.