CD5 Expression in a Lymphoma of the Mucosa-Associated Lymphoid Tissue (MALT)-Type as a Marker for Early Dissemination and Aggressive Clinical Behaviour

Mucosa associated lymphoid tissue (MALT) developing in response to chronic infection or autoimmune stimuli has been recognized as a possible site of origin for a distinct type of B-cell lymphoma. While preferentially occurring in the stomach, MALT-type lymphomas can be found in virtually all organs. MALT-type lymphomas normally follow an indolent course, with a tendency to remain localized at their site of origin for a prolonged period of time. Histologically, MALT-type lymphomas are heterogeneous covering a cytological spectrum ranging from centrocyte-like cells to smaller lymphoid cells or monocytoid B-cells. Usually a small number of transformed blasts are also present. Immunohistochemically, the malignant cells express markers of B-cell lineage, but are distinct from follicular lymphomas (which express CD10), mantle cell lymphomas (expressing cyclin D1 and CD5) and small lymphocytic lymphoma, which express CD5 and CD23. In contrast to the usual phenotype CD20+CD10-CD5-Cyclin D1-, scattered reports in the literature have documented expression of CD5 in marginal zone B-cell lymphomas of MALT-type. However, these cases are rare, and aberrant CD5-expression has been thought to be a marker for early dissemination and aggressive behavior in some patients, while other reports have also found CD5 expression in localized indolent MALT-type lymphomas. We report a patient with a CD5+ MALT-type lymphoma following an aggressive clinical course without histological progression who relapsed only 18 months after local radiotherapy at the initial localizations (conjunctiva of the right upper eye lid and hypopharynx), and showed a rapid generalization to the contralateral conjunctiva, mediastinal lymph nodes and the esophagogastric junction. Our case lends further support to the notion that CD5+ MALT-lymphomas arising in the head-and-neck area and/or the ocular adnexa might be characterised by an aggressive clinical course.