Understanding Surgical Margins in Breast Cancer

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

As part of treatment for breast cancer, surgical removal of the cancer is often required. To remove the tumor, two types of surgery may be done—a mastectomy, in which the entire breast is removed, or a lumpectomy, in which the tumor and some surrounding tissue are removed.

If you require a lumpectomy for breast cancer, your surgeon will remove the tumor and a border of normal tissue around it. This border is called the surgical margin. A pathologist will then examine this margin to determine if all the cancer cells in that area are gone.

If cancer cells are found anywhere between the tumor itself and the outer edge of the margin, additional surgery may be recommended. The goal of negative margins at surgery is to reduce the risk of breast cancer returning in that area, called a local recurrence.

This article will review the use of surgical margins in breast cancer treatment, and how surgical margins impact breast cancer surgery.

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 tumor is usually "inked" on the edges. This allows the pathologist to clearly see the end of the tumor.

A guideline put out by three national cancer organizations recommends removing a margin of 2 millimeters. However, some practitioners may consider removing a 1 millimeter or less rim of healthy tissue. You may want to ask your surgical oncologist what their definition of "clear margin" is.

Using wider margins does not necessarily prevent local recurrence better than using narrower ones in women who have a lumpectomy followed by radiation.

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

A lumpectomy with clear margins may be the only surgery needed to treat breast cancer.

Positive margins, on the other hand, may indicate that all of the cancer was not removed, and another surgery in the same area may be needed to remove more tissue.

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 to get negative margins.

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 was 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 cancer.


Determining surgical margins with breast cancer surgery is very important for the oncologist to know. The goal of removing the tumor is to reduce the risk of cancer returning in the future. Having negative, or clear margins can reduce the risk.

Positive or close margins may require additional surgery for the surgeon to feel confident that all of the cancerous tissue was removed.

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.

Frequently Asked Questions

  • What are good margins after a mastectomy?

    Good margins are generally an area of healthy tissue after cancer has been removed. The exact size of the clear margin may depend upon the surgeon's judgment.

  • What is a positive margin?

    A positive margin means there are cancer cells at the edge of the tissue that was removed. This could mean that there are still cancer cells left in the body.

  • What is a positive biopsy margin?

    A positive margin from a biopsy means that there could still be cancer cells in the body that were not fully removed during the biopsy.

  • What are clear margins in breast cancer?

    Clear margins in breast cancer mean that enough healthy tissue surrounding the cancerous tissue was removed during surgery. This is usually the goal of breast cancer surgery.

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. Pilewskie M, Morrow M. Margins in breast cancer: How much is enough? Cancer. 2018;124(7):1335-1341.

  2. Morrow M, Van Zee KJ, Solin LJ, et al. Society of Surgical Oncology-American Society for Radiation Oncology-American Society of Clinical Oncology consensus guideline on margins for breast-conserving surgery with whole-breast irradiation in ductal carcinoma in situ. Pract Radiat Oncol. 2016;6(5):287-295. doi:10.1016/j.prro.2016.06.011

  3. BreastCancer.org. Re-Excision Lumpectomy

  4. American Cancer Society. Mastectomy

Additional Reading

By Julie Scott, MSN, ANP-BC, AOCNP
Julie is an Adult Nurse Practitioner with oncology certification and a healthcare freelance writer with an interest in educating patients and the healthcare community.

Originally written by Pam Stephan
Pam Stephan is a breast cancer survivor.
Learn about our editorial process