Muco-epidermoid tumours of the anal canal.

The pathology of 21 cases of muco-epidermoid carcinoma of the anal canal is described. These tumours are defined as squamous or transitional cell carcinomas containing areas which secrete mucin of undoubted epithelial origin within the clumps of tumour cells. They are found in that part of the anal canal just above the dentate line where the epithelium is variable in type and represents an embryological transition between rectal and squamous mucous membrane. The histogenesis of these tumours is discussed and the opinion given that they arise from the surface epithelium of the upper anal canal rather than from the anal glands.