[Squamous cell carcinoma on seborrheic keratosis].

To the Editor: Seborrheic keratosis is one of the most common benign epidermal tumors in dermatologic clinical practice. Although the association between seborrheic keratosis and other skin tumors was first reported in 1932, its malignant transformation is very rare, with less than 20 published cases. We present the case of a patient with seborrheic keratosis that underwent transformation into an invasive squamous cell carcinoma. The patient was a 94-year-old woman who was seen in our outpatient clinic for a tumor on the abdomen that had been present for 30 years and that had increased in size over a period of months, causing pain and bleeding. On physical examination, a seborrheic keratosis with a maximum diameter of 12 cm was observed. On this lesion there were several hemorrhagic, lobulated tumors (Figure 1). Complete excision of the lesion was performed, with closure by tissue planes and primary suture under local anesthesia. Microscopic examination revealed different histological patterns within the same lesion (Figures 2 and 3), with images characteristic of ulcerated seborrheic keratosis, areas of transition between seborrheic keratosis and Bowen disease, and zones where Bowen disease infiltrated the dermis (invasive squamous cell carcinoma). The histological diagnosis was of invasive squamous cell carcinoma on seborrheic keratosis. Genotyping for human papillomavirus (HPV) was positive for type 59 in 1 of the 4 blocks sent. The patient remains disease-free after 1 year of follow-up in our clinic. Seborrheic keratosis is rarely associated with other skin neoplasms such as basal cell or squamous cell carcinoma, Bowen disease, keratoacanthoma, or melanomas; in these cases it is most common to find that the lesion is adjacent to or contiguous with the other tumor.2,3 Malignant degeneration of seborrheic keratosis is very rare4 and, when this occurs, it usually develops as Bowen disease and