Molecular insights into the pathogenesis of follicular lymphoma

Abstract

: Follicular lymphoma (FL) represents a group of B-cell neoplasms derived from germinal center (GC) B cells. A better understanding of the pathogenic mechanisms of FL is important for developing innovative therapies. The most common form of FL is primarily nodal and associated with the t(14;18). Recent advances obtained via genomic profiling have provided unprecedented insights into the pathogenesis of FL. Conventional FL evolves through multiple independent or convergent genetic pathways. The classical pathogenesis of t(14;18)-positive FL is a multi-stage and multi-hit process escalating along accumulation of genetic and epigenetic alterations, which starts from FL-like B cells, through premalignant lesions, into full-blown malignancy. Early precursor lesions have been recognized in the form of FL-like B cells in normal peripheral blood, and both in-situ follicular neoplasia (ISFN) and duodenal-type FL. In comparison, t(14;18)-negative FL is much more heterogeneous at the molecular level, and the underlying mechanisms are less well understood. Some variants of FL, while lacking upregulation of BCL2, share a common mutational profile with conventional FL, including mutations in epigenetic modifiers. These cases also show some clinical overlap with BCL2-positive FL, including mainly nodal involvement. Other forms of FL show more profound differences, both clinically and biologically. These emerge more clearly as separate entities and include FL, grade 3B, testicular FL (TFL), pediatric-type FL (PTFL), and primary cutaneous follicle center lymphoma (PCFCL). Mutations in epigenetic regulators and 1p36/ TNFRSF14 abnormalities are highly recurrent and are seen across different subtypes of FL. Genetic profiling has offered important new insights, and will continue to impact the diagnostic approach, with changes in future classification schemes.