CD30+ cell population in common keratoacanthomas: a study of 21 cases.

Many examples of epidermal pseudocarcinomatous proliferations associated to CD30+ lymphoid infiltrates are described in literature. Most of them have been interpreted as epidermal proliferations secondary to the lymphoid infiltrate. In this study, our purpose was to investigate the CD30+ cell population in keratoacanthomas of patients with no other cutaneous or hematological conditions. We randomly selected 21 cases of KA from our archives and performed an immunohistochemical study for CD30 in all of them. The quantity of CD30+ cells was graded according to a 5-tier system (from non-existent to evidence of groups of three or more CD30+ cells each: 0-4). In four cases, the inflammatory infiltrate could not be studied, since the lesions had been enucleated. From the other 17 cases, in 94.12% of them, the infiltrate was graded as 3 or 4. Only one case was graded as 1, and interestingly, this case corresponded to a keratoacanthoma in regression. We also studied the percentage of CD30+ cells in the infiltrate in each case, obtaining a mean of 2.89%. We conclude that CD30+ cells are a common component of the inflammatory infiltrate of normal keratoacanthoma. We also wonder if the cases described as either lymphomas or lymphomatoid papulosis with keratoacanthomatous changes are nothing more but simple keratoacanthomas. Lastly, we see this CD30+ infiltrate as a source of investigation to understand why keratoacanthomas spontaneously regress, instead of progressing to a metastasizing squamous cell carcinoma.