2] Histologically, pagetoid BD is characterized by nests of atypical keratinocytes with round nuclei and abundant pale cytoplasm located either singularly or in groups within the epidermis, and the main differential diagnosis of pagetoid cells
includes extra-mammary pagetoid disease (EMPD) and malignant melanoma in situ (MIS).
Although pagetoid cells
(ample cytoplasm and dusty melanin) are rare, compared with the spindle pattern, pagetoid spreading is common; however, because of the small size of the nucleus, that spreading is not as obvious as it is in other locations.
However, other benign and malignant tumors which can be characterized by intraepidermal pagetoid cells are also in the pathologic differential diagnosis of clear cell SCC in situ (Table 1).
Several conditions, including tumors with intraepidermal pagetoid cells, mimic the pathologic appearance of clear cell SCC in situ.
The pathologic differential diagnosis of clear cell squamous cell carcinoma in situ includes extramammary Paget disease, mammary Paget disease, benign and malignant tumors characterized by intraepidermal pagetoid cells, and other clear cell neoplasms of the skin.
Pathologic differential diagnosis of clear cell squamous cell carcinoma in situ: conditions with intraepidermal Pagetoid cells Clear cell papulosis Clear cell squamous cell carcinoma in situ Clear cells of Toker (of the nipple epidermis) Extramammary Paget disease Cutaneous T-cell lymphoma Eccrine porocarcinoma Histiocytosis X (Langerhans cell histiocytosis) Langerhans cell microabscess (in cutaneous delayed hypersensitivity reactions) Malignant melanoma in situ (superficial spreading) Merkel cell carcinoma (with pagetoid intraepidermal spread) Metastasis (epidermotropic) Pagetoid dyskeratosis Paget disease (extramammary and mammary) Sebaceous carcinoma Spitz nevus (pagetoid) Table 2.
7] When these pagetoid cells are unusually abundant, they may cause concern in inexperienced pathologists.
We have recently observed several cases with pagetoid cells in the squamous epithelium of surgically resected hemorrhoids.
Pagetoid cells were more numerous in the parabasal and midzone layers than in the superficial layers of the squamous epithelium.
The pagetoid cells did not stain with special stains such as periodic acid-Schiff, Alcian blue, Mayer mucicarmine, and Fontana-Masson silver.
The term pagetoid cells includes all discrete non-malpighian or abnormal malpighian intraepidermal cells that resemble cells of Paget disease occurring singly or in small groups in the squamous epithelium.