but occurring in a lab, it's just a similarly fucked up beef muscle cell

And in said lab, you would absolutely make the distinction that it is from a line of cancer cells. If you've altered and engineered it to the point where it no longer has any of the characteristics of cancer cells, then okay. But if you just take a cancer cell out of an organism it absolutely does not stop being a cancer cell just because it left the organism.

I understand the linguistic sleight of hand here, but people just absolutely do not speak of things that way in the real world.

A cell outside of an organism can't be related to a disease by definition.

This just in, pathologists all around the world suddenly unemployed because tissue samples no longer recognizable.