Abstract
We present histopathological criteria for diagnosing keratoacanthoma (KA). In KA, four histological stages are recognized, which are the early/proliferative stage, well-developed stage, regressing stage and regressed stage. In diagnosing KA, we emphasize that KA consists of the proliferation of enlarged pale pink cells with ground glass-like cytoplasm without nuclear atypia, other than crateriform architecture. KA sometimes exhibits malignant transformation within the lesions. We describe the characteristics of benign and malignant epithelial crateriform tumors that should be differentiated from KA. We also present the data of histopathological diagnosis of lesions clinically diagnosed as KA, its natural course and related lesions after partial biopsy, and incidence of crateriform epithelial neoplasms. Based on these data, we recommend complete excision of the lesion when KA is clinically suspected, especially when the lesion is located on a sun-exposed area of an elderly patient. If complete excision is impossible, partial excision of a sufficient specimen with intact architecture is required. In such a case, however, careful investigation after biopsy will be needed, even if the histopathological diagnosis is KA, because there is some possibility that a conventional SCC lesion remains in the residual tissue.
Highlights
Accepted: 5 October 2021Keratoacanthoma (KA) often occurs in a solitary form and exhibits a distinct clinical and histopathological presentation [1]
It is highly important that excisional biopsy or partial biopsy including the center and both sides of KA be performed for correct histopathological diagnosis
We previously reported cases having the same components as conventional KA without the crateriform architecture as keratoacanthoma en plaque/nodule [14] (Figure 1)
Summary
Keratoacanthoma (KA) often occurs in a solitary form and exhibits a distinct clinical and histopathological presentation [1]. KA is either a benign lesion or a distinct borderline malignant entity that is fundamentally different from conventional SCC and features follicular (infundibular/isthmic) differentiation characterized by the involvement of continuous multi-follicular infundibula [7,8,9,10,11,12] They emphasized that KA consists of the proliferation of enlarged pale pink cells with ground glass-like cytoplasm without nuclear atypia, at least in a part of the lesion, and it relatively frequently exhibits malignant transformation.
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