The basal cell nature of the so-called transitional cloacogenic carcinoma of anus as revealed by electron microscopy

Electron microscopic examination of a classical example of so-called transitional cloacogenic carcinoma of anus in a 56-year-old man disclosed ultra-structural features of its component cells to be more coincident with those noted in basal cell carcinoma of skin than in transitional cell carcinomas of the urinary bladder except those with obviously squamous foci. This information does not militate against the origin of these anal carcinomas from the transitional zone of the anorectal junction but does represent evidence relating its cytogenesis to basal cells rather than transitional (stratified columnar) epithelium per se. The terms basal cell carcinoma or basaloid carcinoma of anus appear most appropriate for its designation.