[General principles of the electron microscopic analysis of human neoplasms (using the example of studying lung...

Electron microscopic examinations of lung cancer showed the tumor cells to be capable of specific ultrastructural differentiation owing to which a tumor represents a combination of cells with different degrees of differentiation. This capacity of tumor cells to specific ultrastructural differentiation and formation of tumors consisting of nondifferentiated cells alone or of nondifferentiated and differentiated cells of one or several types, as well as the discovery of differentiated cells simultaneously with signs of cells of two types (chimera cells) suggest that either polypotent (stem cells) or monopotent (precursor cells) cells undergo malignancy. Accordingly, the histogenetic (cytogenetic) appurtenance of a tumor depends not upon its development from one to another type of differentiated cells but upon further direction of differentiation of transformed cells.