TORONTO, Canada--The benefits of annual mammography screening for women aged 50 and over are undisputed, but experts are still polarized over whether the screening procedure is worthwhile for women aged 40 to 49.
Prominent specialists debated the issue at a controversy session at the annual meeting of the American Association for Cancer Research (AACR), with one researcher suggesting that development of tests to improve interpretation of the ambiguous mammograms often seen in younger women could someday render the discussion moot.
Possible Risks of Screening
Making the case against mammography screening for women in their 40s was Karla Kerlikowske, MD, a primary care physician and epidemiologist at the University of California, San Francisco.
In her analysis of 13 international breast cancer studies (JAMA, January 11, 1995), Dr. Kerlikowske found that regular mammography screening did not significantly decrease breast cancer mortality among women aged 40 to 49.
She informs her patients in this age group that there is no proof that mammography decreases breast cancer deaths and that there are risks to undergoing screening, such as the possibility of inconclusive tests and the risk of unnecessary diagnostic tests that cause anxiety and discomfort.
"For a 40-year-old woman who elects annual screening for 10 years, I tell her that she has a 25% chance of having an abnormal mammogram during those 10 years. There is a 23% chance of a false positive, and a 6% to 7% chance of biopsy. But the chance of cancer being detected is only 1.5%," she said.
Because of the large numbers of ambiguous, inconclusive mammograms and false positives, many women must undergo additional expensive tests. "It's estimated that thousands of unnecessary biopsies are performed each year. And all of this causes distress in patients," she said.
Dr. Kerlikowske said that up to 40% of women who have abnormal mammograms will have anxiety for 3 months. The small group that needs to undergo biopsy may have anxiety for up to 18 months. And in that group, the anxiety may persist even after the woman learns that she has nothing to worry about.
She is also concerned about the false reassurance resulting from a false-negative mammogram. She fears that a woman who detects a lump after a normal mammogram may not seek further screening.
Virginia Ernster, PhD, of the University of California, San Francisco, who moderated the debate, is herself a woman in the disputed age group. She has elected not to have annual mammograms.
There is nothing magical about age 50, she said. She suggested that regular screening could start earlier or later, depending on menopausal status, but "physicians may find it easier to ask a woman her age than her menopausal status."
The Case for Screening
Coming out firmly in favor of early screening to aid detection was Edward A. Sickles, MD, a radiologist at the University of California, San Francisco. Recent reports suggest an 8% drop in breast cancer mortality for Caucasian women 40 to 49 years old, he said, and mammography may be partly responsible.
As for the existing data suggesting that screening is not beneficial in this age group, he contends that the studies may be statistically invalid for younger women because breast cancer mortality is so low in this age range.
He added that the most recently published compilation of international breast cancer studies, using, he said, more recent data than those presented by Dr. Kerlikowske, shows a statistically significant 24% reduction in breast cancer mortality for mammography screening of women aged 40 to 49 (Smart CR et al: Cancer, April, 1995).
Dr. Sickles noted that mammography may be discouraged in this age group because the denser breast tissue of younger women can obscure tumors and make the procedure less accurate. But he thinks this argument is negated by improvements in mammography techniques that allow physicians to "see more in the images," he said.
To Dr. Dutzu Rosner, of the State University of New York at Buffalo, the answer to the question of mammography in the 40s is really improved adjunctive imaging techniques that would help physicians interpret ambiguous mammograms in this age group.
Dr. Rosner and his team are studying a radioactive isotope attached to a monoclonal antibody that zeros in on breast tumors. Dr. Rosner, who presented his research at the conference, believes that this method could be an important back-up to ambiguous mammograms.
To date, in the studies at Buffalo, radioimmunodetection has proven 83% to 100% accurate in predicting which ambiguous mammograms are not breast cancers, depending on the type of monoclonal antibody used.
He cautioned that the results are very preliminary, with only 19 women studied so far. However, he said, these results are similar to those reported in January in a European study, which found no false-positive tests in 31 women studied.
A paper describing the Buffalo study has been accepted by Cancer Investigation, he said, and is scheduled for publication in the fall of this year.