Squamous cell carcinoma in situ (Bowen's disease) is an early form of squamous cell skin cancer. In situ means that the cancer involves only the top layer of skin and does not invade or harm surrounding healthy tissue (non-invasive).

Bowen's disease may involve any area of the body but most frequently occurs on sun-exposed areas of the face, neck, arms, and legs. Bowen's disease occurs in sharply defined, round to irregular reddish patches.

People with Bowen's disease may be more likely to develop other cancers, including other skin cancers, or cancers of the lung and gastrointestinal tract.