Read more about this disease, some with Classification – Types – Signs and symptoms – Genetics – Pathophysiology – Diagnosis – Screening – Prevention – Treatment and management – Cures and much more, some including pictures and video when available.
Keratoacanthoma is a relatively common low-grade malignancy that originates in the pilosebaceous glands and closely and pathologically resembles squamous cell carcinoma (SCC). In fact, strong arguments support classifying KA as a variant of invasive SCC. The pathologist often label KA as “well differentiated squamous cell carcinoma, keratoacanthoma variant. KA is characterized by rapid growth over a few weeks to months, followed by spontaneous resolution over 4-6 months in most cases. KA reportedly progresses, although rarely, to invasive or metastatic carcinoma; therefore, aggressive surgical treatment often is advocated. Whether these cases were SCC or KA, the reports highlight the difficulty of distinctly classifying individual cases.[1]
The etiology is unknown. No human papillomavirus-DNA sequences were detected in lesions by polymerase chain reaction. It is a disease of the elderly (mean age, 64 years) with an annual incidence rate of 104 per 100,000. It is not associated with internal malignancy. There may be a seasonal presentation of keratoacanthoma that suggests that ultraviolet radiation has an acute effect on the development of KA. KAs may develop in sites of previous trauma. Most cases are the “crateriform” type, which grow rapidly then undergo spontaneous regression. Less than 2% belong to the rare destructive variants with no regression and persistent invasive growth. These are referred to as keratoacanthoma marginatum centrifugum and mutilating keratoacanthomas and can lead to severe defects.
KA begins as a smooth, dome-shaped, red papule that resembles molluscum contagiosum. In a few weeks the tumor may rapidly expand to 1 or 2cm and develop a central keratin-filled crater that is frequently filled with crust. The growth retains its smooth surface, unlike a squamous cell carcinoma. Untreated, growth stops in approximately 6 weeks, and the tumor remains unchanged for an indefinite period. In the majority of cases it then regresses slowly over 2 to 12 months and frequently heals with scarring. The limbs, particularly the sun-exposed hands and arms, are the most common site; the trunk is the second most common site, but KA may occur on any skin surface, including the anal area. On occasion, multiple KAs appear, or a single lesion extends over several centimeters. These variants resist treatment and are unlikely to undergo spontaneous remission.
According to a review of literature by Robert A. Schwartz, KA was once considered a benign neoplasm that resembled a highly malignant one (pseudomalignancy), but it is now viewed in an opposite light as a cancer that resembles a benign neoplasm (pseudobenignity). KA is an abortive malignancy that rarely progresses into an invasive SCC. The KA may serve as a marker for the important autosomal dominant familial cancer syndrome, the Muir-Torre syndrome, as a result of a defective DNA mismatch repair gene.[2]
Diagnosis is best done with the clinical exam and history. Usually the patient will notice a rapid growing dome shaped tumor on the sun exposed skin. A skin biopsy must be performed to confirm the diagnosis. Unfortunately, a shave biopsy will often only revealed keratin fragments. A deep punch biopsy will often revealed well differentiated mildly atypical squamous cell suggestive of an actinic keratosis or a squamous cell carcinoma. Only when the pathologist has access to the entire lesion (not practical in many circumstances) can a correct diagnosis be rendered. From a practical standpoint (insurance reimbursement), the correct diagnosis should be dictated as “well differentiated squamous cell carcinoma, keratoacanthoma variant”. This is especially important for facial and nasal KA’s, as it allows the surgeon to treat the tumor with the proper respect it deserve with margin controlled surgery like Mohs surgery. Correct diagnosis often require the communication between the surgeon and the pathologist. Many pathologists are still under the impression that keratoacanthomas are benign growths, that does not require surgery. This is reflected in recent edition of this page, arguing for KA to be called a benign tumor. Unfortunately, when the lesion appears on the nose, face, or hands – it often grow to marble or golfball size before necrosing, and leaving a sizable crater in the process. From this practical standpoint, the correct diagnosis of low grade squamous cell carcinoma should be rendered after communication between the surgeon and pathologist is made. As the tumor is often much more aggressive and the morbidity is much higher than the relatively benign basal cell carcinoma.
On the trunk, arms, and legs, electrodessication and curettage often suffice. Excision of the entire lesion if often required if one wants to confirm the clinical diagnosis of keratoacanthoma. On the nose and face, Mohs surgery allows for good margin control with minimal tissue removal; unfortunately, many insurance companies require the correct diagnosis of a malignancy before allowing such procedure. Recurrence after electrodessication and curettage can occur and is frequent, and usually can be identified and treated promptly with either further curettage or surgical excision. Allowing the KA to grow and necrose spontanously is not acceptable in today’s standard of care.
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