Clonal evolution and relapse in early-stage follicular lymphoma - a tree with many branches.

Follicular lymphoma (FL) is an indolent B-cell neoplasm characterised by multistep evolution from premalignant precursor cells carrying the hallmark t(14;18) translocation in the majority of cases. In a new article in The Journal of Pathology, samples of relapsed early-stage FL - primary manifestation and relapse with or without transformation - initially treated with radiotherapy only, were studied for clonal relationships and evolution. Using somatic mutations and the rearranged immunoglobulin sequences as markers, the majority of paired lymphoma samples showed so-called branched evolution from a common, possibly premalignant progenitor cell, with both shared and private mutations. In addition, clonally unrelated cases were identified. This and previous studies with similar findings clearly document that relapse or transformation of FL in many instances not necessarily represents a linear progression of disease due to acquisition of additional mutations and therapy resistance, but rather new outgrowths derived from a pool of clonally related, long-lived, and low proliferating precursor cells, or even unrelated second neoplasms. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.