Keratoacanthoma
Overview
A benign form of skin tumor that tends to resolve itself with time. Usually the skin lesion grows for about six weeks, remains stable for a variable length of time and then regresses slowly.
Symptoms
* Scarring * Flesh-colored skin nodule
Causes
* The definitive cause of KA remains unclear; however, several potentiating factors should be considered. * Epidemiologic data of KA is notably similar to SCC and Bowen disease (BD; SCC in situ) concerning age, sex, and the anatomic site of lesions. This data strongly supports a common etiology among KA, SCC, and BD. Epidemiologic data support sunlight as an important etiologic factor. * Industrial workers exposed to pitch and tar have been well established as having a higher incidence of KA, as well as SCC. * A recent study suggested a strong association between cigarette smoking and the development of KA. * Trauma, human papilloma virus (specifically types 9, 11, 13, 16, 18, 24, 25, 33, 37, and 57), genetic factors, and immunocompromised status also have been implicated as etiologic factors. See Human Papillomavirus. * Recent work has identified that up to one third of keratoacanthomas harbor chromosomal aberrations. Recurrent aberrations include gains on 8q, 1p, and 9q with deletions on 3p, 9p, 19p, and 19q. One other report identified a 46,XY,t(2;8)(p13;p23) chromosomal aberration.
Diagnosis
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.
Treatment
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.