Histogenesis of keratoacanthoma: histochemical and immunohistochemical study.

Objectives: Keratoacanthoma (KA), a keratinocytic neoplasm, is associated with sun exposure and is often found in the head and neck area, including the lip. KA is thought to arise from hair follicle cells, but its origin is largely unknown. Keratins (Ks) and histochemical stains are of great value to characterize and identify normal and neoplastic cells. The objective of this study is to analyze a panel of Ks and periodic acid-Schiff (PAS) staining on KA.

Study Design: Using KA biopsies from the lips and normal skin samples, we performed immunohistochemical and histochemical profiling to determine which biomarkers are conserved between tumors and normal tissues.

Results: The normal hair follicle has multiple well-defined compartments. The outer root sheath (ORS) cells presented K6 and K14 and were also PAS positive. In addition, the infundibulum cells showed positive labeling to K10. Hair cortex keratin was observed in the cortical and precortical cells. Interestingly, KA tumor cells were positive for PAS, K6, K10, and K14 but not to hair cortex keratin. Lip and skin epithelium were negative for PAS and K6.

Conclusions: Our results indicate that KA of the lip is derived from ORS cells, particularly those cells associated with the upper ORS.