Extranodal marginal zone B-cell lymphoma of the skin: A morphologic and immunophenotypic study of 11 cases

Extranodal marginal zone B-cell lymphoma (MZBL) is a recently recognized lo w-grade lymphoma that has been well described in other organs such as the s tomach and salivary gland. It has only recently been described in skin, whe re it may be difficult to distinguish from reactive processes and other typ es of B-cell lymphoma such as follicle center lymphoma. These cases may hav e been classified as pseudolymphomas in the past. Extranodal MZBL was refer red to as mucosa-associated lymphoid tissue (MALT) lymphoma before the Revi sed European-American Classification of Lymphoid Neoplasms was published in 1994. Important histologic features that aid in the diagnosis of MALT lymp homa are atypical lymphocytes (centrocyte-like and monocytoid B cells) ofte n admired with plasmacytoid lymphocytes, a prominent plasma cell component, lymphoepithelial lesions, intranuclear inclusions (Dutcher bodies), and re active germinal centers that may be colonized by neoplastic cells. Immunoph enotypic studies demonstrating a B-cell phenotype, light chain restriction, coexpression of CD43, and staining of atypical lymphocytes with bcl-2 supp ort a diagnosis of MALT lymphoma. We studied 11 cases of extranodal MZBL of the skin from the Armed Forces Institute of Pathology files. There were si x women and five men ranging in age from 30 to 69 years (median, 54 years). The anatomical sites included the trunk, head and neck areas, and upper ex tremities. There were no other sites of disease besides the skin in any of the cases. The follow-up period ranged from 5 months to 8 years (median, 24 months). Histologic results included an atypical lymphoid infiltrate with B-cell phenotype, reactive germinal centers, and a variable plasma cell com ponent in all cases. No Dutcher bodies or lymphoepithelial lesions were not ed. Extranodal MZBL of skin is a diagnostic challenge because of a heteroge neous cellular infiltrate that may be interpreted as a reactive process. Th e most significant neoplasm with which it is confused is follicular lymphom a. It is important to recognize the characteristic histologic and immunophe notypic features of extranodal MZBL so that the appropriate therapeutic app roach may be applied.