Diagnostic Utility of TUNEL Staining for Degenerative Keratoacanthoma Requiring Pathologic Differentiation from Seborrheic Keratosis.

Tumors developed in 2 old women presented with pathological findings similar to seborrheic keratosis, although the clinical feature of tumor showed typical keratoacanthoma. In addition to these two cases, we compared the pathological findings of a total of four cases, one case each of keratoacanthoma and seborrheic keratosis, which were clinically and histopathological typical. These two cases and the typical keratoacanthoma showed cell apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and infiltration of cytotoxic T cells. The keratoacanthoma in the decompensated stage may be histologically similar to seborrheic keratosis. TUNEL staining can help in the diagnosis of fading keratoacanthoma.