Bowen’s disease is the premalignant form of squamous cell carcinoma, in which the cells have become ‘malignant’, but have not left their normal confines. Simply stated, it is ‘cancer’ that has not metastasized yet, in situ. Bowen’s disease must be removed, usually by curettage or excision to prevent the 100% chance of become more aggressive squamous carcinoma and penetrating through its normal confines.

Bowen's disease of the skin, showing the cancerous cells, dark purple as they have high DNA content, versus the light coloured cells, pink, in the periphery. You can see that the cancerous cells have not yet invaded the lower tissue.