Keratoacanthoma

**Semantic type:** Neoplastic Process

**Definition:** A dome-shaped, rapidly growing neoplasm composed of well differentiated squamous cells. It almost always affects the skin and usually occurs on sun-exposed areas of the body, most often the head, neck, and limbs. Rare cases have been reported in extracutaneous sites including the conjunctiva, subungual space, and vulva. It is considered a variant of well-differentiated squamous cell carcinoma with distinct clinical behavior.