it is a good example of phony science, the promotion of which has given false hope to many, and riches to a few. (please note that although I am a surgeon with many years of experience treating breast cancer, I'm not the "official" answer provider here, so you will want to wait for the nurse's response.)
Dear Dulin, Radioactive cesium (cesium-137) is used in certain types of radiation therapy for cancer patients. However, there is no scientific evidence that non-radioactive cesium chloride supplements have any effect on tumors, and there have been some side effects reported.
The American Cancer Society has a good document on their website discussing cesium chloride you can access the document by going to their website at www.cancer.org and typing cesium chloride in the search box.