Reactive Keratoacanthoma Following Treatment with 5-Fluorouracil

Keratoacanthoma (KA) is an epidermal cell tumor with a central keratin plug known to be a variant of keratinocyte carcinoma (KC). KAs typically arise from ultraviolet (UV)-damaged skin and thus are particularly prevalent on extremities. KAs can also be a consequence of local skin trauma. 5-fluorouracil (5-FU) is a topical therapy used to treat early KC, as well as actinic keratoses (AKs). In this paper, we describe the unique cases of two elderly female patients who were treated with 5-FU for AKs of the lower extremities but developed severe inflammatory reactions and reactive KAs to the topical therapy.