http://www.aacr.org/home/public--med...ses.aspx?d=822
Using the CellSearch System techique that quantifies circulating tumor cells, researchers had shown that chemotherapy with Taxol causes a massive release of cells into the circulation, while at the same time reducing the size of the tumor, explaining that complete pathologic responses do not correlate well with improvements in survival.
Circulating tumor cells (CTCs) are cancer cells that have detached from solid tumors and entered the blood stream. This can begin the process of metastasis, the most life-threatening aspect of cancer. To metastasize, or spread cancer to other sites in the body, CTCs travel through the blood and can take root in another tissue or organ.
In this stem cell research, anti-cancer treatments often effectively shrink the size of tumors, but some might have the opposite effect, actually expanding the small population of cancer stem cells that then are capable of metastasizing.
Even before the advent of the CellSearch technique, it had been observed in "cell death" cell culture assays, that there was an increase in the number of metabolic activity of mitochondria of the surviving cells from Taxol therapy, even in cases where the majority of the cells are being killed by Taxol. It may indeed give clinical response (tumor shrinkage), however, these are mostly short-lived and relapses after a response are often dramatic.