Primary malignant melanoma of the gall bladder.

A case of primary malignant melanoma of the gall bladder is reported, in which a 29 year old man presented with acute cholecystitis which led to perforation of the gall bladder and biliary peritonitis. To help in the differentiation between primary and secondary malignant melanoma in the gall bladder and to overcome some of the difficulties posed by the clinical identification of what is often a small or relatively inaccessible primary tumour, it is suggested that certain criteria should be fulfilled before primary melanoma is diagnosed. (i) Tumours must be solitary and arise from the mucosal surface of the gall bladder; (ii) they must either be papillary or polypoid; (iii) they must either display junctional activity or have any other primary sites excluded by history taking, examination, and investigation. If these criteria are applied to the published case reports of primary malignant melanoma, only six cases, including the present one, can be regarded as true primary tumours.