The ultrastructural and immunohistochemical heterogeneity of CD-30-positive neoplasms: so-called anaplastic large cell Ki-1 lymphomas

Anaplastic large cell lymphoma (ALCL), also referred to as Ki-1 lymphomas, was first recognized as an entity with characteristic light microscopic appearance in 1985. This tumor is composed of variably cohesive cells, often with large, markedly atypical, and multinucleated cellular forms. The recognition of ALCL resulted from the development of a monoclonal antibody in Kiel, Germany, named Ki-1, which was initially believed to be a putative marker for Reed-Sternberg cells. This antibody was later found to be specific against the epitope CD-30. Attempts to create strict criteria to preserve this neoplasm as a specific entity have undergone evolution. However, it is now clear that included in this group are a variety of pleomorphic neoplasms with CD-30 immunoreactivity. Some of these neoplasms are nonlymphoid and show marked heterogeneity in their immunohistochemical and ultrastructural profiles. This article aims to highlight the ultrastructural spectrum of neoplasms exhibiting CD-30 positivity that are within the spectrum of ALCL. It remains to be determined if there are subgroups of these CD-30-positive neoplasms that can be segregated on the basis of ultrastructural and immunohistochemical criteria with corresponding clinical correlates that may impact on their management, treatment, and prognosis. We review here the heterogeneity of CD-30-positive neoplasms (so-called anaplastic large cell Ki-1 lymphomas).