In vitro systems such as cell and tissue culture are the primary alternatives. Cell culture is less expensive than the use of whole animals and is easier to manipulate. For example, cancer-causing effects of radiation have been studied in cell culture. Changes in the growth of cells are good indicators for revealing when normal cells become tumor-producing. Some aspects of cancer research require whole animal studies cells cannot mimic the physiology of a live animal.
Clinical studies involving humans are another alternative.
In vivo, in vitro, and clinical studies all combined produce the most informative results. Recent Breakthroughs . Research with both human patients and animal models is in progress, seeking to devise improved methods of treating cancer. With the development of recombinant DNA technology and gene therapy, a functioning gene is inserted into the cells of a patient in order to correct a genetic defect or to introduce a new function into the cell. This technique was approved for clinical trials in the late 1980s.