Cutaneous B-cell Lymphomas

Clinical features and history Cutaneous B-cell lymphomas usually present as one or more erythematous papules or nodules that may coalesce to form plaques. They are usually localized tumors effecting one cutaneous region and rarely ulcerate. There is some regional predilection for various sub-types of tumors; follicle center lymphoma more commonly arises on the scalp, marginal zone B-cell lymphomas usually occur on the trunk or extremities, and the more aggressive diffuse large B-cell lymphoma usually arises on the lower leg. Histomorphology In contrast to malignancies of T lymphocytes which frequently show epidermotropism, the tumor cells in cutaneous B-cell lymphomas spare the epidermis and are usually separated from it by a grenz zone of uninvolved dermis. Immunophenotype Some observers have proposed that a cutaneous lymphomas develop in the setting of a persistent inflammatory reaction or immune dysregulation. This hypothesis has been applied not only to Tcell proliferations in the setting of connective tissue disease, chronic actinic dermatitis (actinic reticuloid), and lymphomatoid drug eruptions, but also has been used to explain the development of cutaneous B-cell lymphomas in the setting of borrelia infection and tattoo. As with T-cell lymphomas, an aberrant B-cell immunophenotype supports the diagnosis of lymphoma, as may be seen in light chain restriction or co-expression of CD43 and CD20. Because the responder cell in cutaneous inflammatory processes is usually a T cell, most non-neoplastic cutaneous infiltrates are composed almost exclusively of T cells. Thus, when B cells comprise >75% of the dermal infiltrate a diagnosis of cutaneous B-cell lymphoma is favored. On the other hand, dense reactive T-cell infiltrates are frequently present in cutaneous lymphoma; in some cases of B-cell lymphoma the neoplastic B cells may represent only a minor component of the dermal lymphocytic infiltrate. An immunohistochemical panel including CD20, CD3, CD21, CD10, bcl-2, and bcl-6 is often useful in distinguishing follicle center lymphoma from marginal zone Bcell lymphoma. Gene Rearrangements The southern blot method of detecting T-cell receptor and immunoglobulin gene rearrangements may yield negative results if the tumor cells represent less than 5% of the sample. PCR based techniques are reported to be positive in most cases of cutaneous T-cell lymphoma but only 50% of cutaneous B-cell lymphomas. As with any diagnostic tool, the interpretation of the genetic results should be in the context of the clinical, histologic and immunophenotypic findings of the case. Treatment and Prognosis