Keratoacanthoma (KA) is a common skin tumor originating in the hair follicle. Although often considered low-grade with a tendency toward spontaneous resolution, its appearance and cellular structure closely mimic aggressive skin cancers. Its rapid development and strong resemblance to squamous cell carcinoma (SCC) necessitate careful and prompt medical identification. Understanding its appearance and behavior is crucial for managing this distinctive skin lesion.
Visual Characteristics of the Growth
A keratoacanthoma typically presents as a solitary, firm, dome-shaped nodule on sun-exposed skin, commonly the face, hands, or arms. The lesion is often symmetrical, with smooth, reddish, or skin-colored edges. This initial papule grows quickly, generally reaching between one and three centimeters in diameter.
The most distinctive characteristic of a mature KA is the central crater, giving it a volcano-like or crateriform appearance. This depression is filled with a dense plug of keratin, the protein that makes up hair and nails. The presence of this hyperkeratotic core, sometimes described as a horn, is the hallmark feature distinguishing KA from other lesions.
The Rapid Life Cycle
The progression of a keratoacanthoma is defined by a predictable three-phase life cycle, separating it from most malignant tumors. The first stage is the proliferative phase, marked by extremely rapid expansion over six to eight weeks. During this time, the lesion grows quickly to its full size of one to three centimeters.
This fast growth is followed by the mature or stabilization phase, where the lesion maintains its dome shape and central crater for several weeks or months. The final phase is involution, where the tumor spontaneously begins to shrink and regress. This natural healing process often takes four to six months to complete, typically leaving behind a depressed, atrophic scar. Because regression is unpredictable, clinicians rarely rely on observation alone for management.
Clinical Distinction from Squamous Cell Carcinoma
The clinical and microscopic similarities between keratoacanthoma and well-differentiated squamous cell carcinoma (SCC) create a diagnostic challenge. Both lesions originate from epithelial cells, leading some pathologists to classify KA as an “SCC, keratoacanthoma-type.” This reflects the difficulty in distinguishing the two based on appearance or partial tissue sampling.
The primary difference is biological behavior: KA tends to regress, while SCC is relentlessly progressive and carries a risk of metastasis. Due to this strong overlap and the danger of misdiagnosing aggressive cancer, most clinicians treat a KA-like lesion with the same caution as an invasive SCC. A definitive diagnosis almost always requires a deep or excisional biopsy to rule out underlying invasive cancer.
Treatment Options and Outlook
Due to diagnostic uncertainty, surgical removal is the standard method for managing keratoacanthoma. Procedures like surgical excision or curettage and electrodessication are frequently employed to ensure complete removal of abnormal cells. For lesions in cosmetically sensitive areas, Mohs micrographic surgery may be used to precisely remove tissue while sparing healthy surrounding skin.
Alternative treatments are sometimes used for smaller or multiple lesions. These non-surgical options include cryosurgery (freezing the tissue) or the injection of chemotherapy agents like 5-fluorouracil or methotrexate directly into the tumor. The prognosis is excellent following treatment, with a low risk of recurrence. If a lesion progresses and metastasizes, it is reclassified as an aggressive SCC, highlighting the need for prompt and complete treatment.