Electron microscopic investigations of progressive early metastasis of cutaneous melanoma.

Primary metastasis of cutaneous malignant melanoma seems to occur especially via the initial lymphatics (IL). In samples of 50 melanomas examined by TEM melanoma cells (MCs), invading IL were demonstrated in 24 specimens. MCs were scarcely found in the immediate vicinity of blood vessels. After the MC has escaped from the MC-complex, connective tissue fibers and cells represent physiological guide-ways that lead the MC to the IL. Located close to the IL, the MC develops pseudopodium-like cytoplasmic processes that penetrate the abluminal fibrous network, fuse partially with the endothelium and destroy it. It seems to be important that the melanomas invade IL as single cells and not in form of cell clusters.