Mammography: lifesaver or not?

by Amy C. Scholten, MPH

To screen or not to screen? That seems to be the latest question surrounding mammography—a widely recommended screening tool in the early detection and treatment of breast cancer.

Use of mammography

Potential screening flaws with mammography

In January 2002, the physician data query (PDQ)—an expert panel of the National Cancer Institute (NCI)—criticized seven previous studies on the benefits of mammography. According to the group, there was insufficient evidence to show that mammograms prevented women from dying of breast cancer. Referring to an analysis of mammography, which appeared in the October 20 issue of The Lancet, the group raised the following concerns:

In younger women (aged 40-49)

Younger women have dense breast tissue, which can make it difficult for lumps and breast changes to be seen on a mammogram. According to the NCI panel, mammograms miss as many as 25% of invasive cancers in 40 to 49-year-old women.

Breast cancer in younger women is also rare (16 cases per 1000 women). A more powerful detection technique and effective treatment would be needed to have a significant impact on the death rate in this age group.

In aggressive (fast growing) tumors

Younger women tend to have more aggressive cancerous breast tumors. By the time a mammogram finds an aggressive tumor, some cancer cells have likely spread to another organ. Therefore, early detection may be too late.

In indolent (slow growing) tumors

Indolent tumors, more common in older women, make up half of all breast tumors. They are usually curable—typically by lumpectomy. According to the NCI panel, these tumors could be detected by breast self-exam, without regular mammograms, and women would have as high a survival rate as the women who do have mammograms.

Screening over the long term

According to Claudia Henschke, a researcher at Weill Cornell Medical Center in New York, mammography screening does not have an immediate effect, but it prevents deaths in the future. Henschke and her team reviewed a Swedish study on mammography published in the British Medical Journal in 1988. They concluded that mammography led to significant reduction in deaths from breast cancer after six years.

However, Danish researchers Ole Olsen and Peter Goetzche of the Nordic Cochrane Center in Copenhagen reported different findings in The Lancet two years ago. After looking at seven studies on mammography, they rejected five of them as flawed. They concluded that mammography is unjustified and that there is no reliable evidence that it reduces deaths from breast cancer.

So, where do we go from here?

The NCI expert panel suggests that evidence in support of mammography is lacking. However, the final verdict on mammograms is not in yet. So once again we arrive at the initial question—to screen or not to screen?

The NCI has consulted with a variety of experts in the field, in order to determine whether a change in its position on mammography is warranted. After careful consideration, the NCI continues to recommend that:

• Women in their 40s should be screened every one to two years with mammography.
• Women aged 50 and older should be screened every one to two years with mammography.
• Women who are at higher than average risk of breast cancer should seek expert medical advice about:
  • Whether they should begin screening before age 40
  • How frequently they should be screened

At the same time, NCI will continue to address the uncertainties surrounding screening mammograms.

Other considerations