Differential diagnoses included intraepidermal adenocarcinoma, in situ squamous or basal cell carcinoma, junctional amelanotic melanoma, and epitheliotropic tumours of histiocytic or lymphocytic origin.
The atypical intraepidermal cells in the cats were immunohistochemically positive for cytokeratin 8/18 (CK8/18), which stains simple (glandular) epithelium.
The keratinocytes and basal cells were negative for CK8/18. In addition, the atypical intraepidermal cells were immunohistochemically negative for melanocytic, lymphocytic, and histiocytic markers.
The staining results confirmed the atypical intraepidermal cells to be of simple glandular origin, and ruled out other causes of intraepidermal malignancy.
In one cat the clinical lesions consisted of a pruritic erythematous eruption surrounding the anus. Another cat presented clinically for an area of irregular anal thickening; this cat had well-regulated diabetes mellitus.
The cats were otherwise clinically healthy. The clinical features, histological appearance, and immunohistochemical staining of the skin lesions were consistent with those described for human perianal extramammary Paget`s disease.
Source: Ann M. Hargis, Audrey E. Baldessari, Emily J. Walder (2007): Intraepidermal adenocarcinoma in the perianal skin of two cats, a condition resembling human extramammary Paget`s disease. In: Veterinary Dermatology (OnlineEarly Articles).
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