Women in the United States are not properly informed about the benefits and risks of mammography and therefore are not able to make an educated decision about whether or not to have the breast cancer screening performed, according to a new study.

Study lead author, Dr. Lisa M Schwartz and colleagues with the Veterans Affairs Medical Center in White River Junction, Vermont, found of particular interest that only 6% of women were aware of a form of usually non-progressive breast cancer known as "ductal carcinoma in situ" (DCIS). However, once informed that mammograms may detect these cancers that may never progress, "60% of women wanted to take into account the possibility of it being detected when deciding about screening.

Researchers did find that most women were aware of false positive mammogram results and viewed them as an "acceptable consequence" of mammography.

The authors conclude that "most women are unaware that screening can detect cancers that may never progress but think that such information would be relevant. Education should perhaps focus less on false-positive results and more on the less-familiar outcome of the detection of ductal carcinoma in situ."

However, an accompanying editorial goes even further, saying that women are even less informed than this study would suggest.

In their opinion, Dr. Karla Kerlikowske and Dr. Virginia L Ernster of the University of California, San Francisco (UCSF) School of Medicine, state that:

It is not clear, however, whether the authors accurately assessed women's true tolerance of false-positive mammography results because their survey did not describe the spectrum of physical and psychological sequelae of a false-positive result (for example, additional diagnostic evaluations and associated morbidity and anxiety).1,2,3

Thus, the proportion of women who are tolerant of false-positive mammography results may have been overestimated because the possible harms of screening mammography were not fully described. Even so, 38% of women surveyed indicated that they would want to factor information about the consequences of false-positive results into their decision about undergoing screening mammography. If nearly 2 of every 5 women desire such information, then they should be informed of the possible harms, as well as the benefits, of screening mammography.  

The editorial notes that the study by Schwartz et al "found that a significant proportion (55%) of women overestimate the benefit of mammography," yet the authors "conclude that the high tolerance for false-positive results is not explained by overly optimistic beliefs of the benefits of mammography." However, Kerlikowske and Ernster think that it is possible that women do overestimate the benefit of screening and that these misperceptions may explain why many women did not want to factor information about the consequences of false-positives into their decision about screening mammography.

They also note that:

... few women (6%) were knowledgeable about ductal carcinoma in situ (DCIS). When women were informed about DCIS, 3 of every 5 women wanted to take into account the chance of it being detected when deciding whether to undergo screening mammography. This is an important finding and suggests that information about DCIS should be included in educational materials and discussions about the possible benefits and harms of screening mammography. 

Kerlikowske and Ernster note that some important information that could be conveyed to women is the absolute benefit of detecting DCIS. "For example, for every 10,000 women aged 70 years and older screened for 10 years, 65 cases of DCIS will be detected and surgically treated with mastectomy or lumpectomy and only 1 death from invasive breast cancer averted," they note.

The editorial concludes that:

To encompass a range of individual preferences, women should be provided with estimates-in absolute terms-of the possible benefits and harms of mammography to make an informed decision about screening. Women who easily tolerate the additional tests that are recommended following an abnormal screening result and want to do everything possible to decrease the chance of death from breast cancer, even if certain harms are involved, will likely choose to undergo screening mammography.

On the other hand, women who feel that the small incremental risk of breast cancer death associated with not being screened is outweighed by the fairly high likelihood of a false-positive result, the additional testing, and the anxiety may rationally choose not to have screening mammography. 

Kerlikowske and Ernster recommend that the following information be provided to a woman for informed decision making before mammography:

• Individual risk of invasive breast cancer and DCIS

• Age-specific chance of an abnormal result

• Age-specific chance of a false-positive result

• Chance that mammography may miss cancer

• Expected absolute reduction in risk of breast cancer deaths among women in her age group who undergo screening mammography compared with women who do not undergo screening

Western Journal of Medicine 2000; 173: 307-312, 313-314

For additional information about ductal carcinoma in situ (DCIS) go to http://mammography.ucsf.edu/inform/index.cfm