Primary cutaneous marginal zone B-cell lymphoma.

Primary cutaneous marginal zone B-cell lymphoma (PCMZL) is included as one of the major types of primary cutaneous B-cell lymphoma in the revised World Health Organization-European Organization for Research and Treatment of Cancer classification. Clinically, PCMZL is an indolent disease and has an excellent prognosis. PCMZL is composed of a polymorphous infiltrate that includes centrocyte-like, monocytoid, and lymphoplasmacytoid lymphocytes and plasma cells. Numerous reactive T cells and lymphoid follicles are commonly associated with the neoplasm. The neoplastic cells express B-cell markers and usually bcl-2 and are negative for CD5, CD10, and bcl-6. Borrelia burgdorferi is a suspected etiologic agent identified in a subset of cases. Although all of these neoplasms presumably are monoclonal, monoclonal IgH rearrangement can only be detected in approximately 75% of cases. Most molecular studies to assess for clonality have used polymerase chain reaction-based methods, and thus this false-negative rate may be attributable to somatic mutation of the IgH variable region genes. Approximately 10% to 20% of PCMZLs have recurrent chromosomal translocations, including the t(14;18)(q32;q21)/IgH-malt1, t(11;18)(q21;q21), and t(3;14)(p14;q32). The t(14;18)(q32;q21) and t(11;18)(q21;q21) have been shown to activate the NF-kappaB pathway.