Marginal zone lymphomas (MZLs) are the most common lymphomas encountered in the orbit and ocular adnexa. The accurate categorization of these lymphomas is critical to avoid undertreatment or overtreatment.
To identify features of orbital MZLs that distinguish them from other lymphomas and reactive lymphoid infiltrates and support the categorization of orbital MZL as mucosa-associated lymphoid tissue (MALT)-type MZLs.
Biopsies from 149 patients with lymphoid lesions of ocular adnexa were examined. Additional immunohistochemical stains and fluorescence in situ hybridization study for the MALT1 locus were performed in selected cases, and patient charts were reviewed.
A total of 115 lymphomas and 34 reactive infiltrates were identified, of which B-cell lymphomas constituted 92% and MZLs constituted 54% of all lymphomas. Certain clinical features (young age, race, bilaterality) favored a reactive infiltrate, but none were diagnostic. Histologic features, such as infiltrative lesions, reactive B-cell follicles, and lymphoepithelial lesions, overlapped between reactive infiltrates and conjunctival MZL. In contrast to conjuctival MZL, orbital MZL infrequently showed reactive follicles, rarely showed epithelial tissue, and did not show lymphoepithelial lesions. Cytogenetic abnormality involving the MALT1 locus was demonstrated in only 15% of ocular adnexal MZLs.
Many MZLs of orbital soft tissue lack key features associated with MALT-type MZL, and the designation MALT lymphoma should be avoided in their diagnosis.