The Who, What, Where, When and Sometimes, Why.

Assessing Margins after Breast Surgery

What is a margin?

When breast cancer is surgically removed (during a surgical biopsy, lumpectomy or mastectomy), a rim of normal tissue surrounding the tumor is also removed. This rim is called a margin.

Margins help show whether or not all of the tumor was removed.

Learn about mastectomy and tumor margins.

Assessing margins after a lumpectomy or surgical biopsy

A pathologist studies the tissue removed during surgery under a microscope and determines whether or not the margins contain cancer cells.

Negative margins (also called clean, not involved or clear margins)

  • The margins do not contain cancer cells on their outer edges. (There’s only normal tissue at the edges of the tissue removed from the breast.)
  • In most cases, no more surgery is needed.

Positive margins (also called involved margins)

  • The margins contain cancer cells.
  • More surgery may be needed to get negative margins. (Discuss this with your surgeon.)
  • Sometimes it’s not possible or necessary to get negative margins due to the tumor location (for example, if it’s at the chest wall or right under the skin).

Close margins

  • The cancer cells approach, but don’t touch the edge of the breast tissue removed.
  • More surgery may or may not be needed, especially with ductal carcinoma in situ (DCIS). (Discuss this with your surgeon.)
  • To further ensure the entire tumor was removed, the removed breast tissue may be X-rayed. This is useful when microcalcifications were found on a mammogram and are related to the cancer. Depending on the X-ray findings, more tissue may be removed at the time of the surgery.
  • If microcalcifications were found on a mammogram before surgery, another mammogram may be done after surgery to ensure all the microcalcifications were removed.

When will I get my results?

You should get your results about a week after surgery.

Mastectomy and tumor margins

With a mastectomy, the whole breast is removed during surgery. Whether the margins contain cancer cells doesn’t usually affect your treatment.

In rare cases after a mastectomy, the deep margin (the margin closest to the chest wall) contains cancer cells. In these cases, more surgery and/or radiation therapy may be recommended.

With a nipple-sparing mastectomy, whether or not the nipple margin (the margin closest to the nipple) contains cancer cells can affect treatment. If the nipple margin contains cancer cells, more surgery and/or radiation therapy may be recommended.

Updated 05/26/22


Fact Sheet

Fact Sheet

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