There exists a weird kind of cancer called a teratoma, whose cells seem to think that they are in an embryo. These cancers differentiate; develop hair, teeth, skin, all manner of messy things. They exist in humans and animals. Some very odd guy wondered if teratoma cells, which seem to want to be an embryo, would actually become one if given a favorable environment. He implanted teratoma cells into an early-stage rat embryo; the teratoma cells there experienced the proper chemical cues and developed into part of a rat. He ended up with a piebald rat – some of the cells had a regular rat mom and dad, while other parts were descended from a cancer propagated in a tissue culture. The rat was fine.Via G. Cochran at West Hunter.
Along the same vein, researchers have found biochemical similarities between the growth of an embryo in a pregnant woman and the biochemical mechanism associated with many cancers. They are trying to figure out how this biochemical process works in order to create a treatment that confounds that mechanism and interrupts cancer-cell specific growth.