We have also been severely hampered by our inability to determine after surgery, radiotherapy or chemotherapy if we got all the cells . Older techniques could measure only one cancer cell in a hundred normal cells. Smaller numbers were missed and treatment was stopped or a necessary treatment not given because the patient appeared free of cancer. Now we have the ability to measure one cancer cell in a million normal cells with newer techniques of molecular biology. We are using these techniques wherever the opportunity presents itself to monitor treatment so we give enough treatment of the right dose, but no more.
Another limitation that affects the use of chemotherapy is the ability of cancer cells to exclude cancer drugs from the inside of the cell, where they do the most damage. Cancer cells can be quite clever. We humans grow up in a world surrounded by all kinds of natural chemicals. Many of them are found in plants or are made by bacteria in soil for the purpose of protecting plants from insects and birds or protecting bacteria from other bacteria. We get our best antibiotics and anticancer drugs from these sources. It should come as no surprise, then, that cells of normal humans, and other species, have developed ways to prevent these chemicals from entering our normal cells in order to avoid being poisoned. The cancer cell regularly usurps these mechanisms to defeat cancer treatment, and we have only recently begun to understand them well enough to develop methods to overcome what we refer to as "drug resistance ." Now we are testing elegant tools to do this.
Finally, the whole field of biologics— the use of natural products—to treat cancer is new. Before the 1970s we could get biologic materials only in very small amounts. With gene cloning now a routine technique, we can turn bacteria and yeast into factories and make virtually unlimited supplies of these materials to test as ways of
