Breast cancer survival has made great strides in recent years, thanks in large part to progress in early detection. Mammograms , or x-rays of the breast, are a widely used tool in early detection. The National Cancer Institute recommends that women forty years and older should be screened with mammography every one to two years.

But despite fairly high levels of mammography screening in the United States—by 1993, 60% of women aged 50 and older had had a mammogram in the previous two years—late-stage breast cancers still occur. The question is whether this represents a failure of the screening process.

In an article published in the October 20, 2004 Journal of the National Cancer Institute , researchers examined that question and found that about half of late-stage breast cancers were diagnosed in women who had not been screened. There was also a substantial group of screened women in whom breast cancer had not been detected. The researchers suggest that making mammogram promotion a priority as well as improving breast cancer detection during screening should reduce late-stage breast cancers.

About the Study

Analyzing data from seven health care plans, researchers selected 1347 women, aged 50 years or older, who were diagnosed with late-stage breast cancer between 1995 and 1999. They defined late-stage as a cancer that was larger than about an inch in size (≥ 3 centimeters) or that had already spread. These case subjects were matched to 1347 control subjects, by health care plan, age, and date of diagnosis. The control patients had been diagnosed with early-stage breast cancer between 1995 and 1999, with early-stage defined as anything other than late-stage. All of the women in the study had access to screening mammography. Women with a previous breast cancer diagnosis were excluded from this study.

The researchers compared the case subjects to the control subjects and, based on their earliest screening mammogram, divided them into three categories:

  • Absence of screening (no mammogram done)
  • Absence of detection (normal/negative mammogram result)
  • Potential breakdown in follow-up (positive mammogram result, but diagnosis of breast cancer more than one year later)

Women with late-stage disease were compared to women with early-stage disease in each category. In addition, the researchers analyzed the demographic characteristics (such as age, marital status, and income) of women with late-stage disease who had not had a screening mammogram.

The Findings

Women who had not had a screening mammogram were more than twice as likely to have late-stage breast cancer as women who had had a screening mammogram. In addition, women with late-stage disease were more likely to not have had a screening mammogram if they:

  • Were 75 years or older
  • Were unmarried
  • Had no family history of breast cancer
  • Had less education
  • Had a median annual income of less than $75,000

The study authors also found that 40% of late-stage breast cancers occurred in women whose mammograms failed to detect their cancer compared with 57% of the early-stage breast cancers. Potential breakdown in follow-up was associated with 8.4% of the late-stage patients and with 8.8% of the early-stage patients.

The study findings were limited by the fact that the researchers chose a control group who had access to screening mammography. Though this control group allowed the researchers to analyze any breakdowns in the care process, it limited their ability to gauge the characteristics and risk of late-stage breast cancer in the general population.

How Does This Affect You?

In this study, absence of screening accounted for about half of the patients with late-stage breast cancer. As a result, the researchers propose making promotion of mammography screening a priority. And because mammograms missed a large percentage of cancer in the late-stage group, the study authors also advocate improving breast cancer detection by the use of new imaging technologies, for example.

But not everyone agrees with this interpretation of the study results. An editorial also published in this issue of JNCI argues that screening mammograms are subject to biases. For example, even though early detection may seem to increase the survival time from diagnosis to death, this does not necessarily mean that early detection actually influences the course of the disease. The editorialist also notes that while some cancers may have been missed by the mammograms in this study, it is more likely that these women had no cancer at the time of their normal mammogram and then went on to develop cancer before their next mammogram. Finally, he argues that even if cost and availability of mammograms are taken out of the equation, as they were in this study, wealthier and more educated women are more likely to have screening mammograms than women of lower socioeconomic and educational status, making it unlikely that promotion will have much impact.

But is there any harm in getting a screening mammogram? Evidence suggests that particularly in younger women, there is a greater likelihood of false positives, which could cause undue anxiety and unnecessary follow-up surgery. On the other hand, breast cancer does occur in younger women, and mammography, even with all its faults, is still the best screening test available for its early detection.

If you are 40 or older, talk with your health care provider about your specific risk factors for breast cancer. Together, you can decide whether a screening mammogram is appropriate for you.