Use of the term 'Cancer' as illness

I understand the word cancer is rooted in the Greek root karkino- (crab). How and when and why did this term come to use in describing tumorous growths of tissue? Anybody?

It’s generally believed to be because many cancerous growths branch out, looking like they’re spreading tendrils throughout the body, so they resemble crabs.

<hijack>

Just because I thought it would be amusing to have 3 posts in a row that had DNA quotes in the sig.

</hijack>

This has already been answered, but here’s an earlier thread anyway: