SYNOPSISThe clinical and pathological features of 15 cases of malignant melanoma of the anal canal are described.It would appear from this study that these tumours arise from squamous epithelium lining that part of the anal canal at or just above the line of the anal valves.Pack, Lenson, and Gerber (1952) MATERIAL AND METHODSA review of all benign and malignant tumours of the ano-rectal region in the records of this hospital is being pursued and has revealed the present total of 15 cases of malignant melanoma of the anal canal seen during this 22-year period. However, 10 of these have been seen in the last 12 years, which perhaps indicates a greater awareness of the diagnosis.In all but four of these patients an operation was carried out for removal of the primary tumour. The surgical specimens were prepared by cutting along the anterior aspect and stretching them out on a metal frame. The specimen was then photographed and the extent of local and lymphatic spread assessed by anatomical dissection and microscopy. Because of this routine method and the museum preservation of some specimens, it has been possible to make an accurate assessment of the exact site of origin of the primary tumour in the 11 cases treated by excision. In particular, the relationship of the tumour to the dentate line or line of the anal valves has been assessed as accurately as possible.All the histological sections were stained with haematoxylin and eosin and the presence of melanin was confirmed by Fontana's ammoniacal silver method.CLINICAL FEATURES AGE The ages of the 15 patients varied from 41 to 75 with an average age of approximately 59 years. This is much the same as the age incidence of adenocarcinoma of the rectum and squamous cell carcinoma of the rectum and squamous cell carcinoma of the anal canal (Morson, 1960b). SEX There were eight women and seven men. In squamous cell carcinoma of the anal canal there is a preponderance of women (Morson, 1960b), whereas adenocarcinoma of the rectum is commoner in men (Dukes and Bussey, 1958). However, Braastad et al. (1949) in their review of the literature report a 126 on 9 May 2018 by guest. Protected by copyright.

SYNOPSISThe 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.Since Stewart, Foote, and Becker (1945) described muco-epidermoid tumours of the salivary glands growths with a similar histological structure have been described in the oral cavity (Smith, Broadbent, and Zavaleta, 1954), uterine cervix (Hellweg, 1957), urinary bladder (Feyrter, 1956), oesophagus (Azzopardi and Menzies, 1962), and anal canal (Kay, 1954 In all but three of these cases the rectum, anal canal, and peri-anal skin were removed by synchronous combined excision. The surgical specimens were prepared in the fresh state by cutting along the anterior aspect and stretching them out on a metal frame. The specimens were photographed and an accurate assessment made of the exact site of the primary tumour as well as the extent of local and lymphatic spread. In particular the relationship of the tumour to the dentate line or line of the anal valves was assessed as accurately as possible.Of the three tumours not treated by excision of the

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