**Core Concept**
Keratoacanthoma is a rare, rapidly growing skin tumor that resembles a squamous cell carcinoma but has a benign course. It is characterized by a rapid growth phase, followed by a spontaneous regression phase. The exact pathogenesis of keratoacanthoma is not well understood, but it is believed to be related to an abnormal response to sunlight.

**Why the Correct Answer is Right**
Keratoacanthoma is most commonly found on sun-exposed areas of the body, such as the face, ears, and hands. This is because exposure to ultraviolet (UV) radiation from the sun is thought to trigger the development of keratoacanthoma. The rapid growth phase of keratoacanthoma is thought to be mediated by the proliferation of keratinocytes, which are skin cells that produce keratin.

**Why Each Wrong Option is Incorrect**
**Option A:** Keratoacanthoma is not typically found on the palms or soles, which are areas of the body that are not typically exposed to the sun.
**Option B:** While keratoacanthoma can occur on the trunk, it is not the most common location.
**Option C:** Keratoacanthoma is not typically found on the mucous membranes, which are areas of the body that are not exposed to the sun.

**Clinical Pearl / High-Yield Fact**
Keratoacanthoma can be distinguished from squamous cell carcinoma by its rapid growth and spontaneous regression, as well as its characteristic appearance, which includes a central crater surrounded by a raised, dome-shaped nodule.

**Correct Answer:** D. Face, ears, and hands.