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.
At higher power of the same lesion, the pleomorphism becomes evident. There is full-thickness dysplasia, with pleomorphism, dyskeratosis, and numerous mitoses. The invasive component appears identical to the epidermis and adnexal epithelium.