CD30+ lymphoproliferative disorders: histopathology, differential diagnosis, new variants, and simulators.

CD30+ lymphoproliferative disorders of the skin (CD30+ LPD) represent a well-defined spectrum of primary cutaneous T-cell lymphomas which have been recognized as distinct entities in recent lymphoma classifications. Lymphomatoid papulosis and anaplastic large-cell lymphoma share the expression of CD30 antigen as a common phenotypic hallmark but differ in regard to their clinical and histologic features as well as their biologic behavior. This article summarizes the histologic features of CD30+ LPD and presents recently identified new clinicopathologic variants of CD30+ LPD. There is an increasing number of reactive inflammatory disorders and neoplastic diseases which are composed of or contain a significant number of CD30+ cells and mimic LyP or anaplastic large cell lymphoma clinically or histologically. Differential diagnostic considerations focus on other lymphoproliferative processes with CD30+ tumor cells as well as non-lymphoid neoplasms and inflammatory simulators. The term CD30+ pseudolymphoma is proposed to designate inflammatory processes with CD30+ T cells. The final diagnosis of CD30+ LPD is based on a synthesis of clinical, histologic, phenotypic, and molecular genetic findings.