New Studies Fuel the Mammogram Debate
It is ironic that during October's National Breast Cancer Awareness Month, and on the eve of National Mammography Day (October 20th), a pair of opposing new studies continue to stroke the debate over the importance-some say effectiveness-of screening mammograms.
According to a controversial presentation at the recent European Breast Cancer Conference in Brussels, screening women for breast cancer more frequently than every three years is likely to have very little additional impact on surviving the disease. Professor Roger Blaney of City Hospital in Nottingham, England reported on a study involving more than 76,000 British women aged 50 to 62 years which compared different screening intervals and their impact on mortality.
After having a standard breast cancer screening, the women in the study were split almost equally between those who would thereafter be screened annually and those to be screened at three-year intervals. During the study, 228 tumors were detected among the 37,530 women in the annual screening group and 196 tumors were detected in the 38,492 women in the three-year screening group.
Interestingly, the researchers did not assess actual mortality over a lifetime but rather made predictions of survival based solely on the characteristics of the tumors they found. On that basis, they predicted that 32.9 percent of the annual screening group and 35.4 percent of the three-year screening group would not be alive at the 10-year point-a 2.5 percent difference in predicted mortality, which was not statistically significant.
Blaney concluded, "there is no significant reduction in predicted mortality from breast cancer produced by annual as against triennial screening," and he added that, "changing to a two-year interval would confer even less benefit."
In stark contrast, another British study, (published in the British Medical Journal just prior to the European Breast Cancer Conference), found that population-wide breast screening "substantially reduces breast cancer mortality."
Dr. S. M. Moss of the Institute of Cancer Research in Sutton, Surrey, UK, and colleagues evaluated data from the British National Health Service breast cancer screening program from 1971 through 1989. They used this data to assess breast cancer mortality through 1998 for women who received screening compared to those who did not.
By 1998, the researchers found that regular screening reduced eventual breast cancer mortality by an average of 14.9 percent in women aged 50 to 54. In the 55 to 69 age group, the reduction in mortality was 21.3 percent. Moss said he expects even greater reductions in mortality due to screening in the coming years. Many more women are being screened, he said, and the sensitivity of screening mammograms has improved significantly.
Dr. Lennarth Nystrom of Umea University in Sweden, writing in an accompanying editorial, said that the study was extremely important because it showed that a national screening program such as the one in the UK, "can have an effect on mortality that is similar to that found in randomized controlled trials."
Further compounding the debate, recent results from a major Canadian breast cancer study concluded that having an annual mammogram plus a clinical breast exam offers no advantage in breast cancer survival compared to having only an annual clinical breast exam. A clinical breast exam is a thorough physical examination of the breast undertaken by a physician.
The findings, appearing in the Journal of the National Cancer Institute, were surprising because of the well-established body of research demonstrating that mammograms can catch breast tumors at much earlier, more treatable stages-when they are often too small to be felt. The researchers, led by Dr. Anthony Miller of the University of Toronto, acknowledged that mammography screening would help catch cancers earlier than just a clinical breast exam. But they wanted to see what long-term impact such additional screening would have on breast cancer survival.
As expected, they found that having a mammogram plus a clinical breast exam more than doubled the detection rate for breast cancer, from 3.45 per 1,000 to 7.20 per 1,000. Furthermore, the tumors that were found with mammography were more likely to be small and less likely to have spread to the lymph nodes.
However, after a long follow-up period, this early detection advantage seemed to disappear. Surprisingly, the researchers wrote, catching the breast cancer earlier through mammography did not translate into a survival advantage compared to having only clinical breast exams. The numbers of eventual breast cancer deaths over the period were statistically equivalent in both groups of women, whether they had an annual mammogram with their clinical breast exam or not.
Miller's team went out of their way to caution that their findings "do not negate the reported benefit from mammography screening compared with no screening." Rather, they suggested another option for screening women over the age of 50-having an annual physical examination plus the teaching of breast self-examination by skilled health professionals.
The Susan G. Komen Breast Cancer Foundation and many other advocacy groups continue to strongly recommend that all women undertake a monthly breast self-exam beginning at age 20; have a clinical breast exam at least every three years beginning at age 20, and annually after age 40; and have yearly screening mammograms beginning at age 40.
"While not perfect," said Rebecca Garcia, Ph.D., vice president of the Komen Foundation, "mammography is the best known screening tool widely available today."
And in spite of such controversies, the Centers for Disease Control and Prevention reports that more American women over the age of 50 are having mammograms than ever before. It notes that in 1998 nearly 70 percent of women aged 50 and older received mammography screening, compared with 61 percent in 1994. In 1987, only 27 percent of women in that age group reported having had a mammogram.
The American College of Radiology is urging women to register for National Mammography Day on October 20. More than 1,100 accredited mammography facilities will be participating in the annual event, offering discounted or free mammograms. To find a nearby participating center, you can call one of the following toll-free numbers:
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