Growth Regulation of Human Acute Leukemia Cell Populations

Abstract

It was long held that the primary feature of cancer was rapid and uncontrolled growth. In recent years, however, it has become apparent from studies of both animal and human tumors that malignant cell growth is not necessarily more rapid than its normal tissue counterpart. In fact, a general characteristic of the malignant cell mitotic cycle is that it is longer than the mitotic cycle of the normal cell counterpart. Furthermore, it has become evident from animal tumor models in both transplanted and autochthonous form that tumor growth regulatory mechanisms exist (2,7). The characteristic feature of growth regulation is that as the tumor grows in mass, a progressively greater number of cells go out of the cell cycle and become resting cells. These resting cells, however, retain the capacity to return to the mitotic cell cycle upon reimplantation. In many respects, growth in animal tumor models resembles that of cells in a tissue culture having regulatory mechanisms that appear to be density dependent.