Keratoacanthoma
This lesion developed over the course of three weeks. Although the lesion appears to be a SCC, the short history and regular border suggest the diagnosis of Keratoacanthoma.
Features
Keratoacanthomas are defined as rapidly evolving tumours of the skin, composed of keratinizing squamous cells originating in pilosebaceous follicles which resolve spontaneously if untreated. These lesions are in the "lesions with malignant potential" section due to their diagnostic difficulty with SCC.
Clinically, these lesions appear as rapidly growing, raised, circular lesions with well defined margins progressing to central ulceration and eventual resolution. The lesions start as small flesh coloured papules, but rapidly grow in size. The skin overlying the lesions may be red and shiny, with underlying telangiectases. They may grow over 2-3 weeks to a size of 2-3cm, or larger.
Lesions are usually solitary and most commonly affect the face. If the diagnosis of Keratoacanthoma is suspected, regular monitoring (e.g. every 2 weeks) should be employed. Keratoacanthomas usually spontaneously resolve at about 3 months and if the lesion is present for longer than this, then it should be excised due to the possibility of malignancy.
Incidence
Relatively common. It is more prevalent in Caucasians than in dark-skinned races and the Japanese. Males are more commonly affected than females (3:1)
Aetiology
These lesions are thought to be caused by exposure to sunlight. Contact with tar and mineral oil is also thought to lead to an increased incidence. It is thought that keratoacanthoma are rarely associated with certain types of internal malignancy.
Differential Diagnosis
Squamous cell carcinoma. Cutaneous horn.
Treatment
Lesions spontaneously regress, but may leave noticeable scarring. Excision or curettage and coagulation leave a better cosmetic result. Excision should be the treatment of choice if diagnosis is in doubt, as the lesion can then be sent for histology. Note that Keratoacanthomas are very difficult to distinguish from SCCs on histology.
In patients who refuse surgery, radiotherapy or topical 5-fluorouracil (Efudix) have been shown to shorten the course and improve the scar.
