Melanosomes of pigmented basal cell epithelioma.

Electron microscopic examination of a pigmented basal cell epithelioma of scrotal skin revealed many tumor cells and melanocytes which were laden with large packages of melanosomes. In tumor cells these packages were delimited by either single- or double-limiting membranes or were not membrane bound. The matrix of these large complexes was less electron dense and homogeneous than normal, containing electrontranslucent droplets besides melanosomes. No remnants of intracellular organelles such as nucleus, mitochondria or ribosomes could be found. The basal cell epithelioma cells in this case appear to have differentiated toward fetal basal cells and have developed the ability to phagocytize large packages of melanosomes.