Giant keratoacanthoma of the plantar foot: a report of two cases.

KA develops from a rapidly growing, firm, smooth nodule into a mature dome-shaped lesion with a central core filled with keratin that usually degenerates into an involuting keratinous mass. KAs must be differentiated from squamous cell carcinoma. Classically, KA is a benign tumor that is self-limiting. However, there is controversy concerning the aggressiveness of the tumor. Some authors believe there is no way to determine the aggressiveness of the tumors and they should be classified as low grade squamous cell carcinomas (3). Others feel that the risk of malignant transformation is not a serious consideration but misdiagnosis is, due to the histopathologic similarities (31, 33). Overall, the literature shows that solitary and giant lesions should be excised. Excisional biopsy yields a more cosmetic scar and increases the chance for an accurate biopsy diagnosis. Multiple and multinodular lesions should be excised if they have the potential for causing a mutilating deformity but are otherwise treated systematically. If a solitary or multiple lesion which is left to spontaneously resolve shows signs of aggressiveness, even with a biopsy indicating that it is a KA, it should be immediately excised. Solitary and giant KA are usually not considered to be located on the palms and soles. However, with the cases presented here, there are now a total of 4 cases in the literature. Therefore, KA should be included in the differential diagnosis when dealing with rapidly growing tumors on the plantar aspect of the foot.