“When we’re treating breast cancer in general, whether it’s your first, second, or third cancer, the goal of surgery is to be able to remove the tumor with clear margins,” Dr. Rosenbaum Smith tells SurvivorNet. “So clear margins are the mainstay of treating breast cancer.”

A clear margin means that when a pathologist examines the tissue removed during surgery, they find no cancer cells at the outer edge. That’s a sign the surgeon removed all visible tumor.

“So once you’ve done a mastectomy, technically there should be no breast tissue there anymore,” she says.

Why a Mastectomy Can’t Remove Every Breast Cell

Breast tissue doesn’t sit in a neat, self-contained package. It spreads thinly under the skin, toward the armpit, and up toward the collarbone. Surgeons remove as much as they safely can, but microscopic cells can remain.

“So then the question really comes: well, can you get another cancer if you remove the whole breast?” Dr. Rosenbaum Smith says.

“And you know, when you’re doing a mastectomy, you are not removing 100% of the breast cells. You can’t.”

“There can always be a microscopic cell left there, and then that cell decides it wants to turn into a malignancy,” she explains.

RELATED: Should I Have a Lumpectomy or Mastectomy?

Treating a New Cancer After Mastectomy

A cancer that appears in the chest area after a mastectomy may be a recurrence of the original cancer, or it may be an entirely new breast cancer arising from leftover cells. Sometimes it shows up decades later.

“Sometimes people will develop a cancer 20, 30 years down the road, and that really is a new breast cancer that’s developed,” Dr. Rosenbaum Smith says.

The surgical approach follows the same principle as the first operation: remove the cancer with clear margins.

“It’s just removing that area with clear margins,” she says. “So that would be a lumpectomy afterward.”

A lumpectomy removes only the tumor and a small rim of surrounding healthy tissue, rather than the entire area. After a mastectomy, that means the surgeon removes the new cancer from the chest wall or skin, along with enough tissue around it to achieve clear margins.

Depending on the type of cancer and your earlier treatment, your care team may also recommend additional therapy after surgery.

Your doctor should promptly check any new lump, thickening, or skin change on the chest wall or near a reconstruction.

RELATED: Recovering from a Lumpectomy

Questions to Ask Your Doctor

• Did my surgery achieve clear margins?
• What is my risk of the cancer coming back after my mastectomy?
• Do I need any imaging or follow-up exams of my chest wall going forward?
• What changes in my chest or reconstructed breast should prompt me to call you?
• If a new cancer develops, would a lumpectomy be enough, or would I need other treatment?

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