transmissible cancer, some surgeons had got cancers from thier patients by accidentally pricking themselves with a contaminiated instrument, although it was treatable and non issue once the tumor was removed. other forms like transplant patients is another source. rare t-cell cancers like mycosis fungoides, you go from patches, to “plaques” to tumors.

and there has only one case of animal to human cancer, the guy had AIDS and got tapeworm cancer from it, which is the most unusual situations out there.