Molecular pathology of lymphoma.

Ocular lymphomas can be divided into intraocular lymphomas and ocular adnexal lymphomas. The vitreoretinal lymphoma-usually a diffuse large B-cell lymphoma (DLBCL) of high-grade malignancy-is the most common lymphoid malignancy arising in the eye, while the extranodal marginal zone B-cell lymphoma (EMZL), an indolent often recurrent tumour, occurs most frequently in the ocular adnexal tissue. The two lymphoma subtypes differ significantly in their clinical presentation, subsequent course and outcome as well as in their underlying morphological, immunophenotypical and genetic features. The molecular processes involved in DLBCL and EMZL development are complex, and include chromosomal translocations, mutations caused by aberrant somatic hypermutation, sporadic somatic mutations, and copy number alterations, characterized by deletions and amplifications. These lead to alterations in particular signalling pathways, which in turn activate transcription factors, such as nuclear factor NF-κB. This review provides an overview of the histological features of DLBCL and EMZL, and discusses the current insights into the molecular mechanisms underlying the development of these tumours, when they occur systemically and particularly when they arise in ocular tissues.