Ocular Follicular Lymphoma with Marginal Zone Differentiation: A Diagnostic Pitfall Mimicking MALT Lymphoma.

Follicular lymphoma with marginal zone differentiation (FL with MZD) is a rare variant that mimics mucosa-associated lymphoid tissue (MALT) lymphoma. A 64-year-old woman presented with a conjunctival mass that was initially diagnosed as MALT lymphoma. Staging revealed additional pelvic and subcutaneous lesions in the patient. Although a needle biopsy of the pelvic mass showed monocytoid B cells lacking germinal center markers, an excisional subcutaneous biopsy demonstrated follicular dendritic cell networks, germinal center marker positivity, and aberrant BCL2 expression. IgH-BCL2 fusion was detected in all lesions, confirming the diagnosis of FL with MZD. This case highlights the need for integrated clinicopathological and cytogenetic evaluations with adequate tissue sampling to make an accurate diagnosis.