Mantle zone lymphoma: an immunohistologic study of skin lesions.

Mantle zone lymphoma (MZL) is a B-cell proliferation regarded as the follicular variant of intermediate lymphocytic lymphoma (ILL). Neoplastic small lymphoid cells proliferate as wide mantles around atrophic centers of benign appearance. The clinical, histologic, and immunohistochemical features of four cases of MZL, heralded by cutaneous lesions, are described and correlated with the lymph node pattern. All specimens showed extensive nodules in the reticular dermis invading the subcutaneous tissue. They were mainly composed of a proliferation of small lymphocytes with slightly irregular nuclear contours and clumped chromatin, forming wide mantles around small atrophic germinal centers. Serial biopsy specimens in case 1 revealed evolution of the skin lesions from pseudolymphoma into MZL. Their immunohistochemistry was similar to that of lymph nodes and showed that the neoplastic cells were CD5+, CD20+, CD22+, CD25+, CD74+, Leu-8+, HLA-DR+, IgM+, IgD+ with restriction for the lambda light chain, CD10-, and CD71-, whereas the germinal center cells were polyclonal. In three cases many CD38+, PCA-1+ plasma cells were present both in the grenz zone and in bordering neoplastic nodules. The clinical course was chronic. The only death occurred from unrelated causes; one patient is still alive 17 years after onset. Skin lesions may be the only manifestation of MZL for an extended period. The differentiation between pseudolymphoma and other lymphoma subtypes is based not only on the histologic and cytologic features but also on the architecture, followed by immunohistochemical confirmation.