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Interval Breast Cancers Found Between Regular Screening Mammograms Seem More Aggressive

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Breast cancers found in between regular screening mammograms — called interval cancers by doctors — were more likely to have aggressive characteristics than breast cancers found by routine screening, according to a study.

The research was published on Sept. 25, 2020, by JAMA Network Open. Read “Incidence, Characteristics, and Outcomes of Interval Breast Cancers Compared With Screening-Detected Breast Cancers.”

About the study

To do the study, the researchers looked at information from 69,025 women age 50 to 64 who were part of the national breast cancer screening program in Manitoba, Canada, from January 2004 to June 2010.

The researchers wanted to see if the characteristics of the interval breast cancers were different from the characteristics of the routine screening-detected breast cancers.

Overall, the women had 212,579 screening mammograms during the study period.

There were 1,687 diagnoses of invasive breast cancer:

  • 705 were screening-detected breast cancers, meaning they were found within 6 months of an abnormal mammogram result
  • 206 were interval breast cancers, meaning they were found within 2 years of a normal mammogram result
  • 275 were diagnosed in non-compliant women, meaning it had been more than 2 years since the woman’s last mammogram
  • 501 were found outside the official screening program

Compared to screening-detected breast cancers, interval breast cancers were more likely to be:

  • higher stage
  • higher grade
  • hormone-receptor-negative

Characteristics of the screening-detected breast cancers:

  • 63% were stage I
  • 29% were stage II
  • 6% were stage III
  • 1% were stage IV
  • 27% were grade 1
  • 48% were grade 2
  • 25% were grade 3
  • 15% were hormone-receptor-negative
  • 83% were hormone-receptor-positive

Characteristics of the interval-detected breast cancers:

  • 25% were stage I
  • 45% were stage II
  • 24% were stage III
  • 6% were stage IV
  • 10% were grade 1
  • 42% were grade 2
  • 49% were grade 3
  • 33% were hormone-receptor-negative
  • 65% were hormone-receptor-positive

After about 7 years of follow-up, 170 women had died from breast cancer and 55 women had died from other causes. Of the women who died from breast cancer:

  • 20 had screening-detected breast cancer
  • 29 had interval breast cancer
  • 27 were non-compliant
  • 94 had cancer detected outside the official screening program

Compared to women diagnosed with screening-detected breast cancer:

  • Women diagnosed with interval breast cancer were more than 3 times more likely to die from breast cancer.
  • Women who did not comply with routine screening recommendations were about twice as likely to die from breast cancer.
  • Women diagnosed with cancer that was detected outside the official screening program were about 6 times more likely to die from breast cancer

“Our results suggest that compared with [screening-detected breast cancers], hazards of death from breast cancer is 3.5-fold higher for [interval breast cancer] in a woman screened under a systematic screening program,” the researchers wrote. “Similarly, [interval breast cancers] were 6 times more likely than [screening-detected breast cancers] to be of higher grade and about 3 times more likely to be estrogen-receptor negative. A quarter of breast cancers diagnosed in women under such screening program were [interval breast cancers].”

It’s important to know that the study had no information on the women’s breast density, their family history of breast cancer, or whether they had a genetic mutation linked to a higher risk of breast cancer.

What this means for you

The results of this study are troubling. They also reinforce two things:

  • the importance of regular breast cancer screening
  • the importance of knowing your own personal risk of breast cancer

At Breastcancer.org, we believe that a woman’s best chance for detecting breast cancer early, when it’s most treatable, requires coordination of our current screening tools:

  • high-quality mammography
  • clinical breast exam
  • breast self-exam

The reality is that every woman is at risk for breast cancer, and this risk tends to increase over time. It’s important to understand and regularly update your health information related to breast cancer risk throughout your life with your doctor. To get the conversation started, here are some points to talk to your doctor about:

  • family history of breast or other related cancers (ovarian, melanoma)
  • any test results for gene mutations linked to a high risk of breast cancer
  • results of past breast biopsies, even if they were benign
  • personal history of being treated with radiation to the face and/or chest before age 30
  • breast density
  • weight, if you’re overweight or obese
  • level of physical activity
  • any use of postmenopausal combined hormone replacement therapy (HRT)
  • alcohol consumption, if you regularly drink more than 3 alcoholic beverages per week
  • the amount of processed food and trans fats you eat
  • your smoking history
  • whether or not you had a full-term pregnancy or breastfed

If you have a higher risk of breast cancer because of dense breasts, a strong family history, or a genetic mutation, you should talk to your doctor about starting annual mammograms at a younger-than-recommended age and consider other screening tools (such as MRI or ultrasound) to maximize the opportunity for early detection.

For more information on the tests and tools used to screen for breast cancer, visit the Breastcancer.org Screening and Testing pages.

Written by: Jamie DePolo, senior editor


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