Tumor Stem Cells And Malignant Cells, One And The Same
Published 2009 · Biology
Cancer is a proliferative, invasive, and metastatic disease often caused by repeated tissue insults resulting in accumulation of genetic abnormalities that rarely produce malignant cells. The survival of mouse L1210 leukemia was determined for inoculations of 1 cell up to 106 cells. The survival times varied in a log-linear manner with the inoculum cell number from 19 days with 1 cell to 7 days with 106 cells implanted. In preclinical tumor models or in patients, tumor nodules of 108–109 cells are advanced cancer. Malignant cells frequently secrete growth modulatory substances that regulate their growth and alter growth of normal cells. Whether the metastatic malignant cell is the same or significantly different from the primary lesion malignant cell remains a topic of active investigation. Reaching a detectable lesion takes 10 years. Genetic instability produces variants in the primary tumor and metastases that are more heterogeneous than the early disease. The argument that cancer arises only from the tissue stem cell populations and that cancer stem cells comprise perhaps 1 in 100,000 or 1 in 10,000 cells within the tumor leads to the notion that agents that selectively kill cancer stem cells will not decrease the tumor mass. The cells that initiate, sustain, and populate cancers are malignant cells. Cancer stem cell notion is useful if it leads to important research questions and to better therapeutics.