Schematic model of the possible patterns of evolution of FL. The cell of origin of FL and transformed DLBCL could be a cell that has already acquired the t(14;18) chromosomal aberration. After migrating from the bone marrow to the lymph node, this cell could acquire further genetic changes (gc) and subsequently the epigenetic aberrant methylation of the PcG genes (ec) before progressing to tumor (A). Alternatively, epigenetic changes of PcG target genes can occur in the BM (B) or in the lymph node (C) and subsequently evolve into FL or DLBCL after additional genomic events.