By Gary M. White, MD
The keratoacanthoma (KA) is a rapidly growing tumor, usually of the sun-exposed skin that mimics a squamous cell carcinoma (SCC). In fact, the distinction between keratoacanthoma and squamous cell carcinoma, both clinically and histologically, is often difficult.
A rapidly growing nodule that develops a central keratotic core in the sun-exposed area of an elderly person is characteristic. The hands and arms as well as the head and neck are commonly affected. The squamous cell carcinoma may present in a very similar manner as a red-white nodule, often with a hyperkeratotic core. As a rule, the SCC is slower growing than the KA--appearing over several months. Note that the basal cell carcinoma is usually pearly, translucent, and without any keratotic core.
Many studies have been performed to distinguish KA from SCC. Most of these rely on histologic criteria, although various immunohistochemical markers have been added to the toolbox. Unfortunately, many tumors still defy classification. Indeed, some even consider the keratoacanthoma a type of squamous cell carcinoma.
Regardless of whether it is a KA or SCC (and often even the pathologist is not sure even with an adequate biopsy), a C&D of such a lesion which has developed on the sun-exposed skin and is less than 1.5 cm is adequate and appropriate therapy. Thus, a biopsy and C&D may be done in one visit. If other diagnoses are being considered, or a straight line scar is preferred, biopsy alone may be done on the first visit followed by surgical excision. Mohs surgery may be done for large lesions or those in cosmetically sensitive areas.
IL chemotherapy is an alternative treatment option, provided histologic confirmation of the diagnosis has been made. 5-fluorouracil (50 mg/cc undiluted from the vial) and methotrexate (25 mg/cc) are the preferred drugs and are injected at weekly intervals. Smaller lesions may be injected once in the center. For larger lesions, multiple injections about the periphery may be done. If the reduction in size is not at least 50% within 3 weeks, excision should be considered.
Can KAs be followed expecting spontaneous resolution? This is controversial. One proponent allows for this approach if the presenting lesion growth has plateaued or the lesion is shrinking. Then, he argues, it may be closely monitored every 2 weeks for further shrinkage with photography and measurements documenting the progress. If at any point, the regression halts, surgical excision is in order.
The body's own immune system may kill the KA--so called regressing KA.
Curettage and electrodessication of a KA.
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