Possibly related, we humans have what's called 'extra chromosomal DNA', basically small bits of DNA that are *not* part of that bound helix anchored with histones that we call 'chromosomes'. They're not well understood (hardly at all, actually), but their presence in cancer cells means that cancer will be much more resistant to treatment than more usual cancers. It's possible they're working like plasmids in bacteria (horizontal transfer), sharing the secrets to surviving chemo or radiation.
Just something I found interesting...