Herman Suit
Massachusetts General Hospital, USA
Title: Evidence for Existence of a Small Population of Radiation Resistant Stem Cells.
Biography
Biography: Herman Suit
Abstract
There are many data that support the concept of drug resistant stem cell populations. Stem cells as a sub-population of radiation resistant tumor cells are almost generally accepted as a component of human tumors. This has conceptually been extended to the concept that the stem cell population is radiation resistant and is the basis for local regrowth of tumors treated by radiation with intent to cure. There have been no quantitation of: 1] the fraction of tumor cells that are members of this stem cell population; 2] radiation sensitivity of these resistant cells relative to the other tumor cells and 3] micro enviornment of these stem cells. There has not been generated experimental data that supports the concept of a small radiation resistant population of stem cells. In fact, the published data encountered have yielded the opposite of. For example, two experiments, performed in laboratories in different countries, have reported that the TCD50 values [dose to inactivate half of the irradiated tumors] were significantly less for transplants of the recurrent tumors than for the previously unirradiated tumors. Further radiation cell survival curves for numerous mammalian cell lines studied in vitro by measuring survival fraction vs dose for survival fraction of 10-[2-4] provided no evidence of a resistant sub-population. One current paper, found that decreasing the number of endothelial cells in tumors did not alter tumor response. These findings and others will be considered.