Ocular adnexa follicular lymphoma: clinicopathological study of 23 patients

Follicular lymphoma (FL) spans both nodal and extranodal sites, with molecular characteristics that may vary by anatomical location. While nodal FL typically shows BCL2 rearrangement and frequent chromatin-modifying gene mutations (CREBBP, KMT2D), some extranodal FLs lack t(14;18)(q32:q21) and harbour distinct alterations, such as TNFRSF14 mutations. In our retrospective series of 23 ocular adnexal FL (OA FL) cases that include both primary and secondary involvement, an approximately equal distribution of BCL2-rearranged and non-rearranged cases was observed, underlining that the ocular localisation displays features of both conventional nodal and extranodal FL. Mutational analysis revealed a mix of mutations commonly seen in nodal and extranodal FL, with strong CD23 expression correlating with JAK/STAT pathway gene mutations. Most OA FLs followed an indolent course with good outcomes after local therapy, though transformation to diffuse large B-cell lymphoma occurred in a subset of two cases. Our results suggest that OA FL exhibits genetic heterogeneity, combining molecular features from both subtypes, and highlight the importance of thorough staging and individualised therapeutic and surveillance strategies for each patient.