Breast Cancer Surgical Margins

When breast cancer is removed, the surgeon tries to take out all the cancer, plus a rim of healthy tissue around it, which is called the surgical margin or margin of resection. This is to be sure all the cancer has been removed.

A pathologist then looks to see if the margin has any cancer cells in it or close to it. 

Margins have three classifications:

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  Clear, also called negative or clean: No cancer cells are in or close to the margin.

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  Positive, also called involved: Cancer cells are right next to or in the margin.

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  Close: Cancer cells are close to the edge of the margin, but not touching it.

Your pathology report also usually tells you how wide a clear margin is or how close cancer cells are to a close margin.

If the margins are positive, more surgery is usually recommended. If the margins are close, your doctor will look to see how close cancer cells are to the margin when deciding if more surgery is needed. If the margins are clear, more surgery is usually not necessary. 

It’s important to know that the definition of a clear margin can vary from institution to institution. Some doctors want 2 millimeters (mm) or more of healthy tissue between the edge of the cancer and the outer edge of the removed tissue. Other doctors consider a 1-mm rim of healthy tissue — and sometimes even smaller than that — to be a clear margin. As you talk with your doctor about whether your margins were clear, positive, or close, you also can ask how your medical team defines clear.