I work in private cancer research--the top-end stuff that provides specific results for a specific individuals and cancers. Bespoke cures, basically. Our clients are invariably the 0.01% wealthiest people on earth. We do important work that will eventually feed into mainstream cancer treatments. We're not decades ahead of the mainstream--more like three to five years.
Because we need total freedom with minimal oversight, our lab is outside of the legal jurisdiction of the US. I say this now in case anyone decides to pursue the information revealed in this post: it will lead to a dead end.
About three years ago we were all about using hybridised mammal zygotes as cheap stem cell factories, which we would use to create white blood cells targeted at our patients' tumors. The 'fetuses' would never be allowed to grow into anything resembling a living creature--we used specialised detergents to prevent the cells from clumping into differentiated tissues. The result of weeks of cell division was a jello ball fed by a capillary-on-a-chip system that served as a crude placenta.
It's important to note that even under ideal conditions, these hybrids would not grow into terrible half-man half-rat creatures. The hybrid cells contained a full set of rat chromosomes, plus 4 key human chromosomes and human mitochondria. We never grew one to maturity. A 'mature' example would be very unlikely to thrive. Genes are at once random and very precise.
But we did have an unchecked blockage in the detergent dripper to one the fetus-on-a-chip trays, so just this ONE TIME the cells were able to differentiate into things recognisable as very early stage mammalian fetuses. Instead of jello blobs we had a tray of rice-grain sized rat-human hybrids growing on the chips.
We put them in the freezer and started again from scratch. The whole debacle cost us (and the people that make our detergent dripper system!) quite a bit.
I had an opportunity to investigate the 'little fellas' under a microscope a few months later. They looked like rat fetuses with unusually long spines and limb deformities.