Intraepithelial Elastic Fibers and Intracytoplasmic Glycogen: Diagnostic Aids in Differentiating Keratoacanthoma from Squamous Cell Carcinoma

Abstract

A significant statistical difference was found between the incidence of intraepithelial elastic fibers in keratoacanthoma and squamous cell carcinoma arising in actinic keratosis (P < 0.001). There was no significant difference when keratoacanthoma was compared to adenoid squamous cell carcinoma (P = 0.13) and de novo squamous cell carcinoma (P = 0.73). However, in keratoacanthoma intraepithelial elastic fibers were found in areas of pseudoepitheliomatous hyperplasia and in the central keratin plug, as well as in areas of infiltrating, peripheral keratinocytes. In adenoid squamous cell carcinoma and de novo squamous cell carcinoma, the intraepithelial elastic fibers were found only in areas of atypical epithelial cells at the margin of the neoplasm. Intracytoplasmic glycogen was found to be statistically more abundant in keratoacanthoma than in squamous cell carcinoma arising in actinic keratosis (P < 0.001), adenoid squamous cell carcinoma (P < 0.001), and in de novo squamous cell carcinoma (P < 0.001)

Differentiating Squamous Cell Carcinoma from Keratoacanthoma Using Histopathological Criteria

“…Many authors have proposed criteria that could be used in the differential diagnosis of SCC and KA [2, 3, 4, 5, 23, 24, 25, 26, 27, 28, 29, 30, 31]. Nevertheless, there were only few attempts to examine the value of these criteria.…”

“…The following criteria were then determined in all samples (answer: presence/absence): rounded shape (arciform disposition) of the lower part of the tumor [25]; sharp outline between the stroma and the proliferating epithelium; central crater filled with keratin [1, 26]; presence of at least one epithelial ‘lip’ at the lateral part of the tumor [[; clear]; intraepithelial elastic fibers (visible with standard staining) [27, 28, 29, 30]; intraepithelial polymorphonuclear abscesses [5]; ulceration [5]; extension more lateral than downward [24]; extension beyond sweat glands [4]; marked pleomorphism or anaplasia [22]; parakeratosis; dyskeratosis [23]; more than 2 mitoses per high-power field (×40) [23, 24, 30]. …”

Cutaneous Hypertrophic Lupus Erythematosus: A Challenging Histopathologic Diagnosis in the Absence of Clinical Information

“…Intraepidermal elastin seen in HLE has also been observed in both inflamed squamous cell carcinoma and KAs. 11,12 A final confounder is that squamous cell carcinoma is an uncommon late complication of HLE. 8 Interestingly, a recent study suggests that CD123-positive plasmacytoid dendrocytes are abundant at the dermoepidermal junction in HLE, but they are present only as single or rare scattered clusters in squamous cell carcinoma and actinic keratoses.…”

Keratoacanthoma causing beak deformity in a budgerigar (Melopsittacus undulatus)

“…In canine and human KAs, it has been stated that the neoplastic epithelial cells have more abundant cytoplasmic glycogen than those in SCC, which can be confirmed by positive PAS staining (Gross et al 2006;King & Barr, 1980). KAs in human patients should contain more glycogen than normal epidermis; however, when considering individual tumours the amount of glycogen present does not allow differentiation between KAs and SCC (King & Barr, 1980). In this case, cells with PAS-positive cytoplasm were more abundant in the tumour mass than the normal epithelium of the maxillary margin of the beak, which supports the diagnosis of KA but does not allow exclusion of the diagnosis of SCC in the absence of any previous studies comparing glycogen abundance in avian tumours.…”

“…The terms have been used interchangeably in previous literature and it has been suggested by some authors that subungual KAs may be capable of malignant transformation into squamous cell carcinomas (Gross et al, 2006;Hafner et al, 1993;Lovett et al, 1995). In canine and human KAs, it has been stated that the neoplastic epithelial cells have more abundant cytoplasmic glycogen than those in SCC, which can be confirmed by positive PAS staining (Gross et al 2006;King & Barr, 1980). KAs in human patients should contain more glycogen than normal epidermis; however, when considering individual tumours the amount of glycogen present does not allow differentiation between KAs and SCC (King & Barr, 1980).…”