Epidermotropic metastatic squamous cell carcinoma. Report of two cases showing histologic continuity between epidermis and metastasis.

Two unusual cases of squamous cell carcinoma (SCCa) metastatic to skin from distant sites occurred. In both metastatic sites, the malignant squamous epithelium fused with benign surface epithelium, and the resulting transition simulated that typically seen in primary cutaneous SCCa. We believe that this previously unreported phenomenon is an expression of the natural tendency of squamous epithelium to "heal" denuded connective tissue surfaces by proliferation followed by epithelial fusion. Because epithelial continuity can be established between benign keratinocytes and metastatic SCCa, one cannot rely on this single morphologic finding to separate primary from metastatic disease.