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 outer edges of the margins don’t contain cancer cells. (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 the details 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 the details with your surgeon.)
  • To further make sure the entire tumor was removed, the removed breast tissue may be X-rayed at the time of surgery. 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 make sure all the microcalcifications were removed.

If you have any questions about the tumor margins, talk with your health care provider.

When will I know whether the margins contain cancer?

You should get the results about whether or not the margins contain cancer a week after surgery.

Ask your surgeon how you will get your results.

Mastectomy and tumor margins

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

However, 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 is recommended.

Updated 04/08/24


Fact Sheet

Fact Sheet