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Cancer researchers generally refer to it as evolution, and I've never heard any complaints from the population geneticists or evo-devo folks about it, so I don't think it's a tremendously controversial way to talk about it. See for example

https://www.nature.com/articles/s41586-019-1907-7

You might want to read this

https://en.wikipedia.org/wiki/HeLa

the single celled dog might beg to differ.

sometimes a cancer can then survive on its own back as a single celled organism

I've heard that some cancers spread by viruses. Viruses do evolve. No idea if that says anything about cancer evolving.