DIFFERENTIAL EXPRESSION OF DESMOSOMAL GLYCOPROTEINS IN KERATOACANTHOMA AND SQUAMOUS-CELL CARCINOMA OF THE SKIN - AN IMMUNOHISTOCHEMICAL AIDTO DIAGNOSIS

The distinction between keratoacanthoma and squamous cell carcinoma is a common dermatopathological dilemma. Although the mainstay of the di agnosis is still clinico-pathological correlation, many dermatopatholo gists now include keratoacanthomas in the spectrum of squamous cell ca rcinomas, Recent reports, however, have pointed out that keratoacantho ma is ''deficient squamous cell carcinoma'' since it loses the express ion of bcl-2 antigen, consistent with initiation of apoptosis, i.e, it s involution, Electron microscope studies performed in keratoacanthoma s and squamous cell carcinomas also revealed significantly reduced des mosomes in squamous cell carcinoma, but not in keratoacanthoma. A seri es of 38 keratoacanthomas and 62 squamous cell carcinomas of the skin (28 well-differentiated, 21 moderately differentiated and 13 poorly di fferentiated) were stained immunohistochemically with the monoclonal a ntibody 32-2B to desmosomal glycoproteins desmoglein 1 and desmoglein 3. Thirty-five keratoacanthomas showed extensive pericellular desmogle in expression Three keratoacanthomas and 28 squamous cell carcinomass (19 well-differentiated, 1 moderately differentiated) showed focal sta ining, and in 11 squamous cell carcinomas (2 moderately differentiated , 9 poorly differentiated) the staining was negative, The remaining 31 squamous cell carcinomas (9 well differentiated, 18 moderately differ entiated, 4 poorly differentiated) showed juxtanuclear staining, None of the squamous cell carcinomas exhibited the extensive pericellular p attern found in keratoacanthomas. Assessment of staining intensity, by 3 independent examiners, revealed a strong negative correlation betwe en desmoglein expression and degree of dysplasia in the squamous cell carcinomas (p<0.01). This antibody therefore clearly distinguishes the se tumours and may be of value in the differential diagnosis of kerato acanthoma and squamous cell carcinomas in routine histopathology.