Spindle-cell squamous carcinoma exhibiting myofibroblastic differentiation. A study of two cases showing fibronexus junctions.

The features of two spindle-cell carcinomas of the dermis are described with special reference to the presence of fibronexus junctions in tumour cells. The cases were of a 78-year-old man with a left eye-lid tumour and a 78-year-old woman with a naso-labial fold tumour, who had been given radiotherapy 13 years earlier for a clinically diagnosed basal cell carcinoma. Both specimens were slightly ulcerated and polypoid. Histologically, invasive tumour consisted of interlacing fascicles of plump spindled and oval cells, which were positive for several anti-cytokeratin antibodies, epithelial membrane antigen, vimentin and smooth-muscle and muscle-specific actins. Ultrastructurally, tumour cells in both cases contained rough endoplasmic reticulum (prominent in case 1), tonofibrils, desmosomes and smooth-muscle type myofilaments with focal densities. Fibronexus junctions were also present, which correlated with positive staining for fibronectin. This is the first documentation of the fibronexus in epithelial tissue in vivo, and the first unambiguous demonstration in a spindle-cell carcinoma. It extends the known distribution of the fibronexus and expands the ultrastructural spectrum of squamous carcinoma.