A bacterium from the intestines of Japanese tree frogs has "exhibited remarkably potent" tumor-killing abilities when administered intravenously, outperforming current standard therapies and paving the way for an entirely new approach to treating cancer.

TL;DR - Ewingella americana is a git microbe which when injected in mouse veins preferentially accumulates around oxygen starved environment, that is a rapidly divided tumor. it also brings immune response around tumor, so your immune system learns to fight it. Still in Mouse phase. but toxicologically safe so could be done in human soon. almost no major side effects (just inflamation)