Are CD30-positive cells specific for lymphomatoid papulosis?

No. The monoclonal antibody CD30 (Ki-1) was first described in 1982 with positive staining of Reed-Sternberg cells of Hodgkin’s disease. Positive staining was also found in the paracortical cells of reactive lymph nodes. Ki-1 positivity can be seen in primary T-cell lymphomas, anaplastic large-cell lymphomas, regressing atypical histiocytosis, and occasionally pityriasis lichenoides et varioliformis acuta (Mucha-Habermann disease). Ki-1–positive primary cutaneous lymphomas have a better prognosis than Ki-1–negative primary cutaneous lymphomas.

Borchmann P: CD301 diseases: anaplastic large-cell lymphoma and lymphomatoid papulosis, Cancer Treat Res 142:345–365, 2008.