Where did you heard that? The only sources I’ve been able to find about lab-grown meat being made out of cancerous cells are tik-tok videos.
All articles I’ve read talk about it being made out of stem cells.
Not calling you a liar, and you have a point that this is something really new and we do not, in fact, know the long term consequences. But I couldn’t find any reliable source to your claim.
And since I know the meat industry will do anything in its power to stop lab-grown meat from being a thing, I wouldn’t trust just “rumors”.
But I guess we should all be a bit skeptical of any claims both for in favor and against.