The interesting case of Dr Richard Carr posted in the Spot diagnosis section of this website on Friday 19/9 of Bowen's disease arising in a seborrheic keratosis has provoked my concern. I performed some Pubmed search and found several published reports of a variety of malignant tumors arising within seborrheic keratosis including BCC, SCC, trichilemmal carcinoma, porocarcinoma and Bowen's disease.

It seems that these cases represent a mere random collision of two tumors within a single lesion rather than a malignant transformation within a seborrheic keratosis. This is rare but still can exist. I do believe that such lesions will have some clinical concern on the first ground. They will not be straight forward seborrheic keratoses. But anyway the presence of such associations should make dermatopathologists very cautious when examining a seborrrheic keratosis especially when the clinician refer it with a "R/O malignancy" comment. Hope I did not miss one of these lesions !!!!