Three cases of primary malignant melanoma of the alimentary tract.

The malignant melanomas of the gastrointestinal tract, especially their achromatic variants, are rare primary tumors, causing certain diagnostic problems. We report three cases of primary malignant melanomas (two of them being achromatic) of the small intestine and anal canal in patients in their fifth decade of life. For precise diagnosis, a parallel investigation was conducted using histology, histochemistry, immunohistochemistry, and electron microscopy. Consideration is also given to the mechanism of these tumors.