11.   Chemotherapy and radiation are efficient killers of tumor cells.

12.   Chemotherapy and radiation are designed to kill off tumor cells.

13.   Dr. Bouck and her colleagues found the protein in a culture of retinal tumor cells.

14.   Earlier Thursday, the scientists behind the experiments described the findings of tests on plants, proteins and tumor cells performed by the former senator and his colleagues.

15.   Enormous doses can be used without apparent harm to the patient because the virus is designed to kill certain types of tumor cells but not healthy cells.

16.   Estrogen fuels the growth of tumor cells in those cancers that have the estrogen receptors.

17.   Eventually, the tumor cells can spread to other organs.

18.   Eventually, however, the tumor cells become resistant to the hormones, the cancer resumes spreading and causes severe pain.

19.   First, it adds a gene to the tumor cells.

20.   For example, in sub-lethal doses, the toxin has been seen to enter and kill tumor cells.