A tumor with 3 stages
Keratoacanthoma undergoes a proliferative, mature, and involution stage.
In the proliferative stage, there is a rapid increase in tumor size; the tumor can get as big as 10 to 25 mm in diameter in 6 to 8 weeks.1,7
In the mature stage, the tumor stops growing and maintains a typical volcano-like form with a central keratin-filled crater.
In the involution stage, up to 50% of keratoacanthomas undergo spontaneous resolution with expulsion of the keratin plug and resorption of the tumoral mass. The process lasts 4 to 6 weeks, on average, but may take up to 1 year. What’s left behind is a residual atrophic and hypopigmented scar.8
Some lesions persist for a year or more, although the entire process from start to spontaneous resolution usually takes about 4 to 9 months.2,7,8
Is it an SCC or keratoacanthoma?
Histology is the gold standard in diagnosing a keratoacanthoma. A deep biopsy specimen that preferably includes part or full subcutaneous fat with excision of the entire lesion should allow for good histologic interpretation and diagnosis. Keratoacanthoma presents as a downgrowth of well-differentiated squamous epithelium. However, even with a well-performed biopsy, the diagnosis of keratoacanthoma remains challenging due to the lack of sufficient sensitive or specific histological features that can distinguish between keratoacanthomas and SCCs.
As a rule, a normal surface epithelium surrounding the keratin plug with sharp demarcation between tumor and stroma favors keratoacanthoma, whereas ulceration, numerous mitoses, and marked pleomorphism/anaplasia favor SCC. Because of the lack of a universal diagnostic criterion, several experts recommend that all keratoacanthomas be considered potential SCCs and thus treated as such.1,2