What Happens During a Lumpectomy Margin Test?

I believe when they cut the tumor out, they have mapped how much tissue to take beyond the tumor edges and then test that tissue to determine clear margins. That’s how it was explained to me

During a lumpectomy, surgeons remove the tumor along with a small amount of surrounding healthy tissue, and this tissue is immediately examined under a microscope to check if the edges (margins) are clear of cancer cells. This margin testing helps ensure complete tumor removal and guides whether additional tissue needs to be taken during the same surgery, which is an important step in treatment planning.