Understanding Surgical Margins in Breast Cancer

The tissue surrounding a tumor and what it means for your treatment

If you require a lumpectomy for breast cancer, your surgeon will remove the tumor and a border of tissue surrounding it called the surgical margin. A pathologist will then examine the tissue to determine if all the cancer cells in that area are gone or if further treatment is needed. If cancer cells are found anywhere between the tumor itself and the outer edge of the margin, additional surgery may be recommended.

cancer margins
Verywell / Gary Ferster

Margin Sizes

To establish the width of a margin, the pathologist will measure the distance between the outer edge of cancer cells and the edge of the tissue that was removed (the margin).

There is no strict guideline for exactly how wide the margin around a tumor should be. Some healthcare providers consider 2 millimeters (mm) or more of normal tissue to be sufficient, while other practitioners consider a 1 mm rim of healthy tissue, and sometimes less, a healthy margin. You may want to ask your oncologist what their definition of "clear" is.

One 2016 study concluded that using wider margins does not necessarily prevent local recurrence more effectively than using narrower ones in women who receive a lumpectomy followed by radiation. (The term local recurrence refers to cancer that eventually comes back in the same breast or the same area as the original tumor.)

Surgical Margin Findings

A pathologist uses a special type of ink to draw a line along the outer edge of the entire tissue sample before slicing it into thin sections and examining it under a microscope.

The pathologist will use one of three terms to describe what they see:

Finding Definition Need for Additional Surgery
Negative (clear) margins No cancer cells at the outer inked edge of the tissue Not typical
Positive (involved) margins Cancer cells or tumor extends to the edge of the sample Typical
Close margins Any situation in between negative and positive Possible

Next Steps

If you've had a biopsy, your tumor is small (under 4 cm), and your surgical margins are clear, a lumpectomy may be all the breast surgery you need.

Positive margins, on the other hand, may indicate the presence of invasive breast cancer, and you may require re-excision of the margin.

Close margins found after a lumpectomy might require another surgical procedure, called a re-excision. In this case, your surgeon would return to the original site and remove additional tissue to try and get negative margins. Some women with close margins choose to have a mastectomy to remove the tissue, rather than undergo one or possibly two more surgeries.

X-rays and/or a mammogram may be done to confirm that the entire tumor was removed and to determine if more tissue will need to be taken out.

For women who've had a mastectomy, cancer cells in the margins within the breast usually have no effect on treatment decisions, since the whole breast is removed. In rare cases, however, cancer cells may be found close to the chest wall, possibly requiring more surgery, radiation, and/or chemotherapy, depending on the stage and other features of the cancer, including the status of the lymph nodes.

A Word From Verywell

Once you've had a lumpectomy, you'll find out if your surgical margins were negative, positive, or close. This, along with cancer type, stage and lymph node status, will help you and your healthcare provider choose the most effective follow-up treatment for you.

Read more about a phyllodes breast cancer tumor.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Breastcancer.org. Surgical Margins

  2. Barrio AV, Morrow M. Appropriate margin for lumpectomy excision of invasive breast cancer. Chin Clin Oncol. 2016;5(3):35. doi:10.21037/cco.2016.03.22

  3. BreastCancer.org. Re-Excision Lumpectomy

  4. American Cancer Society. Mastectomy

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