Keratocanthoma is believed to arise from hair follicles. The natural history of a typical lesion tends to support this; akin to the growth cycle of a hair, there is a period of rapid growth followed by rapid regression. Another suggested cause for regression is immune 'rejection' but there is little supporting evidence.
Initially within the hair follicle there is thickening of the walls as a result of epidermal overgrowth. This soon impinges upon and destroys the hair shaft. Keratin is produced excessively and this forms a central plug within the lesion. The epithelial cells show evidence of proliferation with many mitoses.
This is followed by a static phase with few mitoses. Finally, regression occurs with the remaining epithelial cells keratinizing. There is an inflammatory reaction in the surrounding stroma. Differential growth ensures that the lesion usually ascends to the surface where the keratinous plug detaches. A scar is the common sequel.
Last reviewed 01/2018