A 70-year-old man presents to your clinic with the sudden onset of hundreds of seborrheic keratoses. Is there any reason for concern?

Yes. This patient may have the sign of Leser-Trélat, which is characterized by the sudden appearance of numerous seborrheic keratoses associated with an underlying malignancy. About one third of patients with this sign may also present with acanthosis nigricans, another potential cutaneous marker of internal malignancy. The most common associated malignancy is an abdominal adenocarcinoma.

Ceylan C, Alper S, Kiline I: Leser-Trélat sign, Int J Dermatol 41:687–688, 2002.