Malignant Melanoma of the Gallbladder

A rare case of primary malignant melanoma of the gallbladder was studied with the electron microscope. Two interesting patterns were observed: numerous melanophages were present in the tumor tissue and wrapped compound melanosomes were found in nonneoplastic mucosal epithelium. The infiltration of melanophages was considered to be a reaction to degenerated tumor cells. Concerning the mechanism of melanosome transport into the epithelial cells, a cooperative action between epithelial and melanoma cells seemed to be the most important factor.