Most commonly occurs as an ulcerated nodule or a superficial erosion on the skin. Variants include:

1. Bowen's disease: Erythematous patch or plaque, often with scale; noninvasive; involvement limited to epidermis and epidermal appendages (i.e., SCC in situ).
2. Scar carcinoma: Suggested by sudden change in previously stable scar, esp. if ulceration or nodules appear.
3. Verrucous carcinoma: Most commonly on plantar aspect of foot; low-grade malignancy but may be mistaken for a common wart.