The distinction between
keratoacanthoma and
squamous cell carcinoma is a common dermatopathological dilemma. Although the mainstay of the diagnosis is still clinico-pathological correlation, many dermatopathologists now include
keratoacanthomas in the spectrum of
squamous cell carcinomas. Recent reports, however, have pointed out that
keratoacanthoma is "deficient
squamous cell carcinoma" since it loses the expression of bcl-2
antigen, consistent with initiation of apoptosis, i.e. its involution. Electron microscope studies performed in
keratoacanthomas and
squamous cell carcinomas also revealed significantly reduced desmosomes in
squamous cell carcinoma, but not in
keratoacanthoma. A series of 38
keratoacanthomas and 62
squamous cell carcinomas of the skin (28 well-differentiated, 21 moderately differentiated and 13 poorly differentiated) were stained immunohistochemically with the
monoclonal antibody 32-2B to desmosomal
glycoproteins desmoglein 1 and
desmoglein 3. Thirty-five
keratoacanthomas showed extensive pericellular
desmoglein expression. Three
keratoacanthomas and 20
squamous cell carcinomas (19 well-differentiated, 1 moderately differentiated) showed focal staining, 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 differentiated, 4 poorly differentiated) showed juxtanuclear staining. None of the
squamous cell carcinomas exhibited the extensive pericellular pattern found in
keratoacanthomas. Assessment of staining intensity, by 3 independent examiners, revealed a strong negative correlation between
desmoglein expression and degree of dysplasia in the
squamous cell carcinomas (p < 0.01). This antibody therefore clearly distinguishes these tumours and may be of value in the differential diagnosis of
keratoacanthoma and
squamous cell carcinomas in routine histopathology.