Malignant melanoma of the gallbladder: report of three cases and review of the literature.

Three cases of primary melanoma of the gallbladder are described to add to the five reported in the literature. As an organ of endodermal origin, the gallbladder appears to share the melanoblastic potentiality possessed by similarly derived organs, and hence, the development of a melanoma within the gallbladder is not unexpected. Presence of melanocytes within the gallbladder mucosa is absolute proof that the tumor is primary. Whether these cells originate from the neural crest and migrate to the gallbladder, or result from local differentiation from preexisting cells remains to be answered.