Interestingly, IL-17 has been shown to activate keratinocyte proliferation in an indirect manner by inducing the expression of IL-19 and heparin-binding EGF-like growth factor (HBEGF) in these cells, thus stimulating epidermal hyperplasia [22,23,24], which is a common histopathological finding in HS lesions [25]. The gene discussed is IL17A; the disease is histiocytic sarcoma.