Expression of desmosomal proteins in acantholytic squamous cell carcinoma of the skin.

Acantholytic (adenoid) squamous cell carcinoma (ASCC) is a subtype of squamous cell carcinoma (SCC) in which neoplastic tumour cells form gland-like structures. Little is known about the pathogenetic mechanisms of ASCC. We hypothesised that they may be related to the compositon of desmosomes. We analysed the immunohistochemical expression of desmosomal proteins in 5 cases of ASCC of the skin, in comparison to 5 cases of conventional SCC of the skin. The most consistent findings were loss of desmoglein 1 (DSG 1), desmoglein 3 (DSG3), desmocollin 1 (DSC1), desmocollin 2 (DSC2), desmocollin 3 (DSC 3), and plakophilin 1 (PKP 1), and decreased expression of desmoplakin 1 (DP 1) and plakoglobin (PG). In conventional well to moderately differentiated SCC, the expression of desmosomal proteins was decreased, but membranous staining was mostly preserved with patterns similar to normal epidermis. Our results suggest that loss of desmosomal cadherins and decreased expression of desmosomal plaque proteins might be responsible for the formation of gland-like structures in ASCC. It seems that desmosomal cadherins, which correspond to the transmembrane core of desmosomes, are predominantly affected in ASCC, while DP 1 and PG, which correspond to cytoplasmic plaque of desmosomes, probably play a lesser role in maintenance of tumour cell cohesion. Our results also indicate that, in addition to previously described verrucous and spindle cell carcinoma, ASCC is another subtype of SCC with a characteristic expression pattern of desmosomal proteins.