RE:RE:RE:FYI - updated corp presentation dated Sept 2021
I'm no expert but from what I've read, there are many cell culture lines for different cancers. You can make them grow in a lab dish. You can measure the cell activity using markers or cell number or mass. If you test an intervention, you always have the exact same cells as a control comparison in an untreated dish.
Other ways to test are to have rodents with transplanted human tumours growing on them.
There is some interesting research in recent years showing that cancers don't behave in people quite the way they behave in dishes. A good response in a dish is a good starting point for sure.