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Evidence that regression in Keratoacanthoma is immunologically mediated: a comparison with squamous cell carcinoma

Recent research observations suggest that the keratoacanthoma (KA) is a form of resolving squamous cell carcinoma (SCC). The mechanism by which this resolution takes place has not been fully explored, although it may have an immunological basis. To investigate this, we compared 15 clinically and histologically diagnosed KAs and 15 SCCs with regard to cellular infiltrate and keratin expression. We found that KAs have significantly higher numbers of CD3+ and CD4+ cells invading their epidermal component than SCCs. The lymphocytes infiltrating KAs were more immunologically active, as greater numbers expressed the interleukin‐2 receptor (IL‐2R) than those in SCCs. It is of interest that CD36 was expressed by a significantly greater proportion of tumour cells within KAs than SCCs. This was also the case for the intercellular adhesion molecule ICAM‐1, and the differentiation marker keratin 10. Overall, these findings suggest that KA regression is immunologically mediated, with activated (IL‐2R+) CD4+ T lymphocytes and adhesion molecules playing a pivotal role in the immune response.