Squamous cell carcinoma can take different forms, depending on the group of cells affected:
- Adenoid squamous cell carcinoma (also called Pseudoglandular squamous cell carcinoma) – an uncommon subtype of squamous cell carcinoma characterized by a reddish lesion, most often on the floor of the mouth.
- Verrucous carcinoma (Ackerman tumor) – this is an uncommon subtype of squamous cell carcinoma. It occurs mostly in people who chew tobacco or use snuff. Unlike basaloid squamous cell carcinoma, verrucous carcinoma is less aggressive, and has a good prognosis.
- Keratoacanthoma – this skin tumor is common in the elderly population; but it is less aggressive. Keratoacanthoma is characterized by rapidly growing red papule (A small solid circumscribed bump rising from the skin) over a few weeks to months.
- Clear cell squamous cell carcinoma (Clear cell carcinoma of the skin) – this is a subtype of squamous cell carcinoma characterized by a clear discoloration of the keratinocytes, cells of the living epidermis and certain oral epithelia.
- Spindle cell squamous cell carcinoma – this is a rare microscopic subtype of squamous cell carcinoma characterized by spindle-shaped atypical cells;
- Basaloid squamous cell carcinoma – this type of squamous cell carcinoma is highly aggressive, and tends to occur in the tongue base, hypopharynx, and supraglottic larynx.
- Signet-ring cell squamous cell carcinoma – this is a highly malignant mucus-secreting tumor characterized by development in the skin of malignant cells having histologic appearance of signet ring cells.