You know, with targeted genetic sequences and wielding benign viruses, this actually has never been that hard. Costly because it's time consuming, yeah, but not actually hard.
SciShow has a good video on this actually. Its based on using Killer T Cells from other patients, as it's found some can be really agressive and can use an MR-1(I think) identifier to find and route out most/ if not all forms of cancer!
*Tiktok gets deleted from people's phones*