A 66-year-old man presents to the clinic for evaluation of a skin lesion on his hand. The lesion has grown rapidly over the previous 2 weeks. He endorses trauma to the area when he accidentally scraped his hand against a window and notes that there was some bleeding. His medical history is significant for chronic renal failure for which he received a renal transplant 5 years prior, as well as multiple surgeries for skin cancer. His current medications include aspirin, atorvastatin, prednisone, tacrolimus, and mycophenolate mofetil. His temperature is 98.6°F (37°C), blood pressure is 136/91 mmHg, pulse is 82/min, and respirations are 11/min. Physical exam is notable for a 2 x 2.5 cm nodular lesion of the dorsal hand as seen in Figure A. Which of the following is the most likely diagnosis?
Keratoacanthoma
Verruca vulgaris
Basal cell carcinoma
Molluscum contagiosum
Keratoacanthoma
This patient presents with a rapidly enlarging, well-circumscribed, volcano-like papule with a central keratotic core consistent with the diagnosis of keratoacanthoma.

Keratoacanthomas represent a well-differentiated variant of cutaneous squamous cell carcinoma. They present as a rapidly enlarging skin lesion with a characteristic hyperkeratotic core. Most lesions occur on the sun-exposed areas of the body, especially the head, neck, and extremities. Risk factors for developing a keratoacanthoma include immunosuppression, arsenic exposure, old scars or burns, xeroderma pigmentosum, or exposure to high levels of ionizing radiation. Most keratoacanthomas tend to involute within several months after initial onset; however, surgical excision can be performed because of the histologic similarity to squamous cell carcinoma. Biopsy of lesions with malignant transformation will show atypical keratinocytes and malignant cells, invasion into dermis, and keratin “pearls” on histology.

Kwiek and Schwartz present a review of keratoacanthoma diagnosis and treatment. They discuss how these lesions characteristically exhibit spontaneous regression after rapid growth. They recommend surgical excision as first-line therapy for the lesion.

Figure/Illustration A is a clinical photograph showing a well-circumscribed, dome-shaped papule with a hyperkeratotic core (red circle) consistent with keratoacanthoma.

Incorrect Answers:
Answer A: Basal cell carcinoma is the most common skin cancer in humans. It most commonly presents as a pearly pink papule or ulcer with telangiectasias and a rolled border. Compared to keratoacanthoma, basal cell carcinomas are slow-growing and are only locally invasive. Surgical excision is the treatment of choice for most basal cell carcinomas.

Answer C: Molluscum contagiosum is a common viral infection caused by a poxvirus that is most frequently seen in children. It presents with solitary or multiple umbilicated papules and is spread by person-to-person contact. Immunosuppressed individuals, such as those with HIV/AIDS, may have disseminated molluscum contagiosum, which is highly recalcitrant to treatment.

Answer D: Pyogenic granulomas are vascular proliferations that present as rapidly growing, pink to red, friable papules that are prone to bleeding with minor trauma. They are most commonly seen in children and pregnant women. The oral mucosa is a common area of presentation, although pyogenic granulomas may present in any skin location. Treatment is through mechanical removal via surgical excision, laser ablation, or electrical curettage.

Answer E: Verruca vulgaris is a common viral infection of the skin caused by several subtypes of human papilloma virus (HPV). They present as rough-textured or filiform papules. Close examination may reveal pinpoint areas of red/black, which represent thrombosed blood vessels within the wart. Treatment options for common warts include salicylic acid or cryotherapy; however, recurrence after treatment is common.

Bullet Summary:
Keratoacanthomas presents as rapidly enlarging, well-circumscribed, volcano-like papules with a central hyperkeratotic core.