Bowen disease is medically the same as "squamous cell carcinoma in situ." Squamous cell carcinoma is a tumor that develops from the squamous cells which are flat, scale-like cells in the outer layer of the skin (the epithelium). The term "in situ" (borrowed from the Romans) means "in the natural or normal place" and, in the case of cancer, it says that the tumor cells are still confined to the site where they originated and they have neither invaded neighboring tissues nor metastasized afar.
The hallmark of Bowen disease is a persistent, progressive, slightly raised, red, scaly or crusted plaque. Bowen disease may occur anywhere on the skin surface (or on mucosal surfaces such as in the mouth).
The cause of Bowen disease classically was prolonged exposure to arsenic. Today, Bowen's disease occurs most often in the sun-exposed areas of the skin in "older" white males.
Bowen disease is named after the American dermatologist John Templeton Bowen (1857-1941).