Background: Distinguishing keratoacanthoma (KA) and hypertrophic lichen planus (LP) histopathologically can be difficult, and the challenge is compounded by the tendency of KA to arise in association with hypertrophic LP.

Methods: In this pilot study, we compared 18 cases each of KA and hypertrophic LP for proliferation index (MIB-1), p53 staining and the presence of perforating elastic fibers (elastic Verhoeff-van Gieson) to determine the utility of these staining modalities in distinguishing KA from hypertrophic LP.

Results: Proliferation index in KA compared to hypertrophic LP is 88.2 (mean positive MIB-1 cells/×100 field), SD = 56.6 and 47.3, SD = 68.4, respectively. p53 staining in KA compared to hypertrophic LP is 251 (mean positive cells/×100 field), SD = 117 and 158, SD = 119, respectively. Fifteen of eighteen (83%) keratoacanthomata demonstrate perforating elastic fibers compared to 1/18 (6%) for hypertrophic LP.

Conclusions: Proliferation index is not significantly different between KA and hypertrophic LP (p = 0.059). Expression of p53 is increased in KA over hypertrophic LP (p = 0.024). The presence of perforating elastic fibers in KA is significantly different from hypertrophic LP (p < 0.0001) and suggests that elastic Verhoeff-van Gieson staining may be of practical benefit in distinguishing KA from hypertrophic LP in difficult cases.