Transformation of seborrheic keratosis into Bowen's disease.

This case proves the possibility of a malignant transformation of seborrheic keratosis. This evidence is furnished by a biopsy specimen that shows not only a topical relationship between seborrheic keratosis and Bowen's disease, but also the progressive transition. An evident biopsy has to be made prior to clinical suspicion of malignant degeneration, that means prior to the destruction of the transitional zone by the tumor.