A Case of Squamous Cell Carcinoma during Treatment of Imiquimod to Common Warts on the Penis

Abstract

A 33-year-old-man noticed warts on his penis from childhood, which gradually spread to the whole head of the penis. He developed phimosis and became unable to urinate due to balanoposthitis. Circumcision was performed more than ten years prior. The physical examination at our department revealed papillary nodules on the glans penis and foreskin. The foreskin was hard and attached to the coronal margin. We diagnosed him with common warts histopathologically. As this case had a wide range, was deep, and caused strong pain, cryotherapy was considered difficult, and imiquimod was administered. Imiquimod was self-applied by the patient to the warts three times per week and left in place overnight. When there was redness, erosion, swelling, or pain, imiquimod was temporarily discontinued, and betamethasone valerate, gentamicin sulfate ointment, or white petrolatum was applied until the symptoms disappeared. At 7 months, although there was some residual, the warts improved and the foreskin was able to retract. However, squamous cell carcinoma (SCC) was observed on the foreskin. No causal relationship between topical imiquimod treatment and the appearance of SCC has been found. There are three case reports of SCC during or after imiquimod treatment for solar keratosis, but no case reports of common warts. In this case,it is highly possible that SCC was lying underneath the warts. Common warts are often difficult to eradicate by current therapies and imiquimod is considered to be an effective treatment. It is important to observe carefully during or after imiquimod treatment, and to perform early skin biopsy if malignancy is suspected. Skin Research, 20 : 216-224, 2021