Mammograms are effective at catching breast cancers early in women with a personal history of the disease, but not as effective as they are in women with no such history, according to the findings of what has been termed the most comprehensive relevant study of the effectiveness of annual screening for breast cancer survivors.

You can read how members of the Breast Cancer Surveillance Consortium carried out the study, and confirmed their support for annual mammogram screening of breast cancer survivors, in a report published online this week in JAMA, Journal of the American Medical Association.

Annual mammography screening is standard surveillance practice for women who survive early stage breast cancer, because they are at risk of cancer recurrence, or a new cancer forming, in either breast. However, there is little documented evidence of how effective it is.

The first author of the study was Dr Nehmat Houssami, an associate professor at the University of Sydney’s School of Public Health and Sydney Medical School in Australia.

“More women are surviving longer after having early-stage breast cancer, but they are at risk of developing breast cancer again, a recurrence, or a new cancer,” said Houssami, who is also a physician at the Royal Hospital for Women, in Australia.

With other colleagues from the Breast Cancer Surveillance Consortium (BCSC), she examined 12 years of data covering 58,870 mammograms in 19,078 women who had had early-stage breast cancer, and the same number of mammograms in 55,315 women with no history of the disease. The two groups were matched for breast density, age, year of screening, and BCSC registry.

“The comprehensive data from the BCSC made it possible for us to carefully examine the outcomes of screening for both the previously affected breast, as well as the opposite breast, at a population level,” said Houssami.

They found that:

  • Women with a personal history of breast cancer had twice the rate of cancer as women with no history.
  • 655 second cancers were observed in women with a personal history of breast cancer (499 invasive, 156 in situ) and 342 cancers in women with no such history (285 invasive, 57 in situ).
  • The cancer rates were 10.5 per 1,000 screens for women with a personal history of breast cancer versus 5.8 per 1,000 for women with no history.
  • Also significantly higher in women with a personal history of breast cancer than women without, were the true-positive detection rate (6.8 versus 4.4), and the rate of interval cancers (3.6 versus 1.4).
  • Screen-detected and interval cancers in women with and without a personal history of breast cancer were mostly early stage.

The researchers concluded that mammography screening in women with a personal history of breast cancer “detects early-stage second breast cancers but has lower sensitivity and higher interval cancer rate, despite more evaluation and higher underlying cancer rate”, relative to that in women with no such personal history.

Houssami said:

“Mammography was effective at finding cancers early in women who had had cancer, but not quite as effective as in those who had not.”

She explained that they found higher rates of both “false positives” and “interval cancers”, and that mammography was not as sensitive at detecting invasive breast cancer, in women with a personal history of breast cancer.

A false positive test is one where the test suggests there is a cancer, but further testing shows this is not the case. Interval cancers are cancers not spotted by mammography that are found between screenings, either from monitoring breast changes or other tests.

Co-author Dr Diana Miglioretti, a senior investigator at Group Health Research Institute in Seattle, Washington, in the US, said:

“Because of the risk of interval cancers, it’s important that women seek medical care for any breast changes or concerns between mammograms.”

“The good news is that most of the breast cancers detected in breast cancer survivors between mammography screens were early stage,” she added.

Because the findings showed that interval cancers were particularly high in women under 50, or who had very dense breasts, or who had undergone breast conserving treatment (a lumpectomy) without radiotherapy for their first cancer, Miglioretti said:

“… we should consider more tailored screening strategies in these women, such as additional or alternate screening modalities in some groups – but this needs further research.”

Funds from the National Cancer Institute in the US (as part of a cooperative agreement with the BCSC), and Australia’s National Health and Medical Research Council sponsorship of the Screening and Test Evaluation Program , helped pay for the study, which was also supported in part by several US state public health departments and cancer registries in the data collection phase.

“Accuracy and Outcomes of Screening Mammography in Women With a Personal History of Early-Stage Breast Cancer.”
Nehmat Houssami, Linn A. Abraham, Diana L. Miglioretti, Edward A. Sickles, Karla Kerlikowske, Diana S. M. Buist, Berta M. Geller, Hyman B. Muss, Les Irwig.
JAMA 2011;305 (8):790-799
DOI:10.1001/jama.2011.188

Additional source: Group Health (press release, 22 Feb 2011), University of Sydney (press release, 23 Feb 2011).

Written by: Catharine Paddock, PhD