Abstract
A precise electron microscopical distinction between so-called mature and immature mast cell tumours is possible. In immature mast cell tumours, the neoplastic cells contain granules in various phases of development, well-developed ergastoplasm, many free ribosomes, extended Golgi apparatus, complex cytoplasmic membranes, and nuclei with folded nuclear membranes, hypertrophic nucleoli, and finely dispersed chromatin. In mature mast cell tumours, the neoplastic cells have scarce ergastoplasm, fewer free ribosomes, a small Golgi apparatus, some cytoplasmic protrusions, and nuclei with predominantly heterochromatin and only a few folds of the nuclear membrane; the cytoplasmic granules are electron-dense and amorphous or reticular or granular or contain membranous structures. The mature neoplastic cells resemble normal tissue mast cells. In the genesis of granules five phases of maturation can be distinguished. The release of substrate may result from dissolution of granules. In experimental degranulation the release of whole granules may be the immediate result of a relatively strong stress and interference with the cell structure. The intranuclear virus-like structures observed (a small virus containing DNA?) are discussed as a possible oncogenic agent.