Presumed primary malignant melanoma of the gallbladder. Report of a case and a review of literature.

Primary malignant melanomas of the gallbladder are rare lesions that have been the subject of debate. Only 11 such cases have been reported. The debate is reviewed and conflicting opinions of workers in the field are discussed. Attention is drawn to some of the features that are said to characterize the lesions presumed to be primary melanomas of the gallbladder, such as polypoid growth, "junctional" changes in the normal mucosa, and, above all, absence of other demonstrable primary foci of malignant melanomas. What at first appeared to be the 12th case of this rare entity, and in the youngest patient at that, is now described by light and electron microscopy, but a more likely possibility, supported by biopsy of the skin, is that an undiagnosed malignant melanoma in the skin had undergone complete regression after it had metastasized to the gallbladder.