Keratoacanthoma: what kind of skin tumor is it and how is it detected

You noticed a nodule on the skin that grew within just a few weeks, and a dense keratin plug appeared in the center. This is what keratoacanthoma may look like — a skin tumor that dermatologists and oncologists discuss separately because externally it can resemble squamous cell carcinoma. Below is a calm breakdown: what this lesion is, how it develops, and which examinations help settle the diagnosis.

What keratoacanthoma is

Keratoacanthoma (KA) is a common, rapidly growing, and locally destructive skin tumor. It may regress spontaneously with scar formation, but clinically it can be indistinguishable from well-differentiated squamous cell carcinoma, and its course can be unpredictable. Therefore, many clinicians and pathologists prefer the term "squamous cell carcinoma, keratoacanthoma type" and recommend surgical excision. The tumor originates from the infundibulum of the hair follicle.

What keratoacanthoma looks like and how it develops

Typical KA is a solitary, rapidly growing nodule on sun-exposed areas of the skin of the face and upper extremities. It is well demarcated, firm, reddish or skin-colored, with a classic central keratin plug and a smooth rolled border. If the keratin core is removed, a crater-like appearance remains. A solitary KA grows over several weeks to 1–2 cm, then remains stable for several weeks and begins to regress, leaving a depressed scar; usually 4–6 months pass from appearance to complete regression. Rare variants also exist, such as centrifugum KA, which expands peripherally with central scarring and is often not prone to regression.

Causes and risk factors

The specific mechanisms are not fully understood; dysregulation of the WNT signaling pathway and mutations in the TP53 tumor suppressor gene are discussed. Risk factors are probably the same as for squamous cell carcinoma:

• ultraviolet exposure;
• chemical carcinogens — smoking, industrial contact with tar, pitch, and mineral oils;
• skin trauma, including surgery and radiation;
• human papillomavirus infection;
• immunosuppression and some genetic syndromes.

KA is more common in fair-skinned older men with chronic sun exposure: most patients are over 60 years of age, and it occurs twice as often in men.

How keratoacanthoma differs from cutaneous squamous cell carcinoma

The main difference is in behavior: KA may resolve on its own with a scar, whereas squamous cell carcinoma grows without treatment and can spread. But by appearance and even by histology, the differences are not always absolute, so the decision is made based on the combination of signs, not on a single examination.

How diagnosis and biopsy are performed

The diagnosis is based on the typical history, clinical signs, and histopathology. At low magnification, classic KA appears crater-like; at high magnification, enlarged atypical keratinocytes with eosinophilic cytoplasm are visible, not extending beyond the level of the sweat glands. Material is obtained by skin biopsy — this is the key step that allows KA to be distinguished from other tumors.

When to see a dermatologist or oncologist

Any suspicious skin lesion and any change in its appearance is a reason to see a doctor: early detection improves outcomes. People see a dermatologist for a rapidly growing nodule, keratin plug, ulceration, or bleeding. Complications of KA include scarring, destruction of adjacent structures, ulceration, and bleeding.

Keratoacanthoma itself is not a reason to call an ambulance; 103 or 112 — if the nodule bleeds heavily and the bleeding does not stop.

This material is for reference and does not replace a doctor's consultation: the decision on management is made by a specialist after examination and evaluation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer