Cellular heterogeneity in human epithelial neoplasms.

Tumor cell heterogeneity has in recent years been the subject of numerous excellent review articles, but comprehensive reviews may not always distinguish between that which is known about tumors from direct observation and that which is inferred from the study of analagous systems. The purpose of this review is to describe what is known about cellular heterogeneity in human tumors and to discuss current models of the pathogenesis of cellular heterogeneity in light of the evidence available from the study of human cancer.