<qa>  What is the name of the research that has shifted from cell lines to animal models?During the last two decades, cancer research has shifted from using cell lines and animal models to directly using human tissue. This is especially true for research focused on premalignancies for which there are few good animal models. Research utilizing human tissues and sera not only addresses many issuesquestions of medical research that cannot be evaluated in cell lines andor in animal models of human disease, but it also provides a system to test the relevance of these findings to human diseases. Various biologic and genetic changes that occur in the developmental stages of human neoplasia can be identified and analyzed using human tissues. 