Why the Rate of Repeat Breast Cancer Surgery Varies So Widely

Surgeons still don't have official guidelines for lumpectomy, one of the most commonly performed breast cancer surgeries, the authors of a new study say.

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Women who undergo lumpectomy for breast cancer end up with widely varying results, according to a new study, because there are no guidelines to help doctors decide how best to perform the procedure.

Lumpectomy involves removing the tumor from the breast, along with a margin of healthy tissue to ensure that stray malignant cells aren’t left behind. But while lumpectomy is one of the most common treatments for breast cancer, there is still no consensus on how large a margin surgeons should carve out.

That could explain why, as a study published in the Journal of the American Medical Association reports, nearly 23% of 2,206 women who underwent lumpectomy at four hospitals across the U.S. had to have a second operation. The additional operation is done when the patient’s pathology report suggests that tumor cells may have been left behind — but because there is no rule for what constitutes a cancer-free “clear margin,” the chance of a second surgery after lumpectomy depends less on the patient than on the surgeon.

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In fact, rates of repeat surgery in the current study varied greatly depending on the surgeon (0% to 70%) and the hospital (1.7% to 21%). The study found further that nearly half of the repeat surgeries were done in women whose pathology reports showed no evidence of residual tumor cells. And 14% of patients who did show such signs of remaining cancer did not have additional surgery to remove it.

“It is getting to be the time for leaders in radiation oncology and surgery to get together and make a consensus statement that could help guide their membership,” Dr. Monica Morrow, chief of breast surgery at Memorial Sloan-Kettering Cancer Center, told the New York Times.

The study’s lead author, Dr. Laurence McCahill, assistant director of the Lacks Cancer Center in Michigan, called the range in results “a shame.”

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Much of the discrepancy has to do with surgeons’ individual judgment and that of the institution where the operation is performed. Some surgeons are more likely to cut conservatively to try to save as much of the healthy breast tissue as possible — and this is a reason repeat surgery is such a problem with breast cancer, but not other cancers for which cosmetic issues are less important — while others are more aggressive and favor larger margins.

Adding to the confusion is the fact that studies on the matter don’t necessarily support intuition. It would seem logical that bigger margins are safer, but recent trials show that may not be the case. Cancer cells may escape to other parts of the breast but not be detectable with mammography or by the surgeon during the operation. What’s more, since nearly all women with breast cancer now receive radiation and chemo or hormone therapy after lumpectomy, the size of the margin matters less in terms of recurrence risk.

That still leaves breast cancer patients and their surgeons with a difficult balancing act. Determining how large a margin to cut may never be an exact science, but establishing some guidelines for doctors to follow when drawing their boundaries could help lead to more consistent results. And that would be welcome news for patients who may be spared having to undergo another surgery.

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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.