Gut Check is a periodic look at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?

The claim: Women with a breast abnormality called ductal carcinoma in situ (DCIS) who do not receive “timely” radiation treatment have a significantly higher risk of developing malignant breast tumors, compared to women who had radiation within eight weeks of their surgery, according to a study presented on Monday at the annual meeting of the American Association for Cancer Research.

Tell me more:

DCIS, which accounts for about 20 to 25 percent (some 60,000 per year) of the breast cancers detected by screening mammograms, used to be considered very early-stage breast cancer, or Stage 0. Recent research, however, suggests it might actually not be cancer at all, but a noninvasive abnormality. That view remains controversial, though, with treatment guidelines continuing to call for lumpectomy or mastectomy followed by radiation.

For the new study, Dr. Ying Liu, a surgeon at Washington University School of Medicine, followed 5,916 women in Missouri who had been diagnosed with DCIS between 1996 and 2011 and underwent breast-conserving surgery. During the six-year follow-up, 3.1 percent of the women developed a tumor in the same breast as the DCIS. The risk was 26 percent higher for women who had radiation more than eight weeks after their DCIS diagnosis, and 35 percent higher for women who did not receive radiation at all. “Timeliness of radiation therapy should be improved,” Liu said, adding that African-American women, single women, Medicaid patients, and those with larger DCIS were more likely to delay treatment.

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Really?

Some of these groups, as well as women without access to high-quality health care, are also at higher risk of breast cancer, anyway. That, and not the delay in radiation therapy for DCIS, could explain their higher rate of later breast cancer. This is a common problem with observational studies, namely, that important differences among two groups (in this case, women who get radiation therapy for DCIS right away, and those who don’t) explain their different outcomes, not the variable (radiation) being studied.

But there is a more fundamental problem. The absolute risk of recurrence is so small that the higher relative risk of 26 percent is grossly misleading, said Dr. Laura Esserman of the University of California, San Francisco, a breast cancer surgeon not involved in the study. Absolute numbers are more meaningful: the difference in risk of developing breast cancer is about 0.8 percent, or fewer than one woman in 100. “This is an example of [a finding that is] statistically significant and clinically irrelevant,” she said.

The new study is also at odds with recent ones, which have been bolstering the revisionist thinking that DCIS is not cancer and does not have to be treated as such (much as elevated PSA readings do not necessarily have to be treated as prostate cancer). A 2015 study of 108,196 women found that 20 years after their DCIS diagnosis, 3.3 percent had died of breast cancer, almost identical to the rate of women generally. And crucially, those who received radiotherapy had the same risk of dying of breast cancer 10 years out as those who did not. “Why should patients use radiation when we know from many studies that it has no effect on mortality?” asked Esserman. (She adds, however, that in African-American women and women under 40, DCIS is somehow different and should be treated according to the more aggressive guidelines.)

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Surgery for DCIS has not reduced the incidence of invasive breast cancers, casting doubt on the conventional wisdom that these are precursors to real malignancies. A 2015 study found that, six years out, 98.6 percent of women who had surgery were still alive, versus 98.8 percent of those who did not, adding support to the idea that DCIS can be managed with active surveillance.

Verdict:

With more and more evidence that most DCIS is not cancer and need not be treated as such, it seems unlikely that a delay in radiation therapy will make a meaningful difference for patients.

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