Huh i guess my memory is trash, what chapter/character confirmed this? It really feels weird especially considering how many people were planetarian-able, not to mention the fact that some of Hwang Ji's abilities were straight up infecting literally everyone like an actual plague, but i guess technically speaking any large multicellular organism is bound to have a wee bit of cancer in it, so maybe that's the excuse and sis here is somehow 100% cancer free.