Over 50 years ago, scientists took a primary colonic adenocarcinoma from a 74-year-old patient, diced it up, and injected it under the skin of immune deficient mice. The tumors grew over several weeks and were then transplanted to another set of mice. The researchers, Rygaard and Povlsen, showed that the tumors retained many characteristics of the original human one. However, getting the tumors to grow in mice wasn’t necessarily an easy task. Of the four tumors they injected, two breast carcinomas and two colon carcinomas, only one took.