This lesion on the chest of a 78-year-old man was submitted to rule out basal cell carcinoma. Some authors differentiate squamous cell carcinoma in situ from Bowen disease, arguing that Bowen disease arises from adnexal epithelium rather than epidermis. This would explain the characteristic adnexal involvement, flat epidermis, and difficulty with topical treatment in Bowen disease. With this argument, actinic keratoses invade as squamous cell carcinoma and Bowen disease invades as adnexal carcinoma, as shown in this case.
Histologic sections of skin show a basophilic cellular proliferation involving the epidermis and infiltrating into the dermis. There is overlying serum crust. The dermal stroma is slightly edematous.