What are Margins in Relation to Breast Cancer?

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Answer: Margins, also known as "margins of resection," refer to the distance between a tumor and the edge of the surrounding tissue that's removed along with it.

When a tumor is removed, some tissue surrounding it is also removed. The tumor with surrounding tissue is rolled in a special ink so that the outer edges, or margins, are clearly visible under a microscope. A pathologist checks the tissue under a microscope to see if the margins are free of cancer cells.

Depending upon what the pathologist sees, the margins of a tumor are described as:

  • Positive margins: Cancer cells extend out to the edge of the tissue, where the ink is.
  • Negative margins: No cancer cells are found in the ink.
  • Close margins: Any situation that falls between positive and negative is considered "close."

Knowing how close cancer cells are to the edge of the removed tissue helps in making the right treatment decisions. This is especially important in deciding whether additional surgery is needed. If the margins are positive, more surgery is needed. If the margins are close, you may or may not need more surgery. If the margins are negative, you probably don't need more surgery.

The definition of "negative margins" varies from one hospital to another. You may want to ask your doctor whether your margins were positive, negative, or close, and how "negative" is defined by your medical team.

To help standardize this definition, the American Society for Radiation Oncology and the Society of Surgical Oncology issued new guidelines in February 2014 saying that clear margins, no matter how small as long as there was no ink on the cancer tumor, should be the standard for lumpectomy surgery.

You can read a detailed discussion and see pictures that will help you understand all about surgical margins.

To get more help in understanding your pathology report, read the transcript of our November 2001 Ask-the-Expert Online Conference, "Your Pathology Report."

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