Pagetoid reticulosis after radiotherapy of primary cutaneous anaplastic large-cell lymphoma.

We describe a 60-year-old man with a history of primary cutaneous anaplastic large cell lymphoma on the chest, who presented with a new scaly red plaque on the same site 11 years after radiation therapy. Histological examination revealed a dense epidermotropic infiltrate of atypical mononuclear cells consistent with pagetoid reticulosis. Immunohistochemistry revealed the infiltrate to be CD4, CD8, and CD30. Remarkably, all the atypical cells were strongly CD30, and furthermore, the CD30 cells were found exclusively in the epidermis. In the initial cutaneous anaplastic large cell lymphoma lesion, the CD4, CD8, and focally CD30 atypical cells were well confined within the dermis with no epidermal component. To our knowledge, the present case seems to be the first description of pagetoid reticulosis presenting at the site of a previously treated dermal anaplastic large cell lymphoma. This case also represents an extreme presentation of epidermotropism and CD30 expression in pagetoid reticulosis.