Interval Breast Cancers Often More Aggressive

By Megan Brooks

October 02, 2020

NEW YORK (Reuters Health) - Interval breast cancers (IBC) - those detected between routine mammography screening - are often more aggressive and more likely to lead to death than screen-detected breast cancers (SBC), a retrospective study from Canada has found.

"Our study re-enforces the fact that screening mammography is far from perfect, detects less aggressive cancers that are less likely to be life-threatening, and that the really aggressive cancers still show up clinically after a normal screening mammogram," Dr. Saroj Niraula, associate professor, University of Manitoba and medical oncologist, CancerCare Manitoba, told Reuters Health by email.

The researchers analyzed data on 69,025 women (ages 50 to 64) who underwent a total of more than 212,000 mammograms between 2004 and 2010. Among the 1,687 invasive breast cancers detected, 705 were SBC, 206 were IBC, 275 were diagnosed in noncompliant women for whom more than two years had elapsed since from their last mammogram and 501 were detected outside the screening program.

Compared with SBC, IBC were much more likely to be high-grade (odds ratio, 6.33; P<0.001) and had three times greater odds of being estrogen-receptor negative (OR, 2.88: P<0.001), the authors report in JAMA Network Open.

After a median follow-up of seven years, 170 women had died from breast cancer and 55 had died from other causes. Among the breast-cancer deaths, 20 had SBC, 29 had IBC, 27 were noncompliant and 94 were detected outside the screening program.

Breast-cancer-specific mortality was significantly higher with IBC than with SBC (hazard ratio, 3.55; P<0.001), with no significant difference in non-breast-cancer mortality.

"The study highlights the caveats of current use of mammographic screening," Dr. Niraula told Reuters Health.

"Strategies beyond routine screening mammography are needed to prevent, detect and avert deaths from the more lethal interval breast cancers," the authors conclude in their paper.

Dr. Stephanie Bernik, chief of the breast service at Mount Sinai West, who wasn't involved in the study, urged caution in interpreting the results. "We can't really draw firm conclusions on their findings, but there are a few takeaway points," she told Reuters Health by phone.

One is that screening mammography should be performed as recommended. "If there is a finding, it should be discussed with the doctor to see if it's worthwhile to biopsy at that time," said Dr. Bernik, associate professor of surgery at the Icahn School of Medicine at Mount Sinai in New York City.

"A lot of it has to do with how you handle the finding initially. We're pretty aggressive here about biopsy when we see new things but you can't biopsy everything. A lot of things are followed because they look benign, and then they turn out to be cancer," said Dr. Bernik.

Echoing Dr. Niraula, Dr. Bernik said the results do indicate that "science isn't perfect."

SOURCE: https://bit.ly/3n4Bwp1 JAMA Network Open, online September 25, 2020.

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