Misperceptions about Mammograms
Controversial results just released from a major Canadian breast cancer study have 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 September 20th issue of 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. Nonetheless, the results cannot be dismissed because of the size of the study (39,000 women) and its long-term nature (a mean follow-up period of 13 years).
"The Canadian National Breast Screening Study-2" had been tracking these women since the mid-1980s, when they were between the ages of 50-59. 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.
They assigned the women to one of two groups: those who would have both a mammogram and a clinical breast exam each year, and those who would have just an annual breast exam.
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 immediately issued a statement calling the study "enlightening," but warned that it highlighted "the need for better methods for early detection of breast cancer and identification of pre-cancerous abnormalities."
As with all forms of clinical studies, the Foundation noted, one study is not enough to change public health policy. They continued 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."
While the Canadian study clearly fuels the ongoing debate over the effectiveness of screening mammography, the fact remains that mammograms are still able to detect small tumors up to two years earlier than clinical breast exams. The earlier cancer is detected, the less likely it will have spread, and the more responsive it will be to treatment.
One major repercussion of the Canadian study-and the skewed media fallout resulting from it-is that it could deter many women from undergoing mammography screening, especially those in certain minority populations which have historically low screening rates.
For example, a recent report in the journal Cancer found that Asian-American and Pacific Islander women have the lowest breast and cervical cancer screening rates of all ethnic groups in the United States. Nearly one-third of the women in these demographic groups have never had a mammogram, compared with 21 percent of Caucasian women. The rates were particularly dismal for Asian Indian women, where 68 percent have never had a mammogram.
Similar studies document significantly lower screening rates for African-American and Hispanic women as compared to Caucasian women, as well as for all women in lower income levels. A recent study by the Centers for Disease Control's National Center for Health Statistics found that only 53 percent of women with family income below the federal poverty level reported having a mammogram within the previous two years.
And a study published in the Western Journal of Medicine found that lesbian and bisexual women are less likely to receive appropriate screening compared with heterosexual women, even when they have similar access to healthcare. Lesbians underwent mammography screening at approximately half the rate of heterosexual women. Bisexual women underwent screening mammography at about one-third the rate.
That same Centers for Disease Control and Prevention study touted that more American women over the age of 50 are having mammograms than ever before. It noted 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.
And yet, that overall success rate has clearly not been realized within many demographic groups outside of Caucasian, heterosexual women. If the media fallout from the Canadian study makes many women believe that mammograms are simply not worth the hassle, years of efforts to reach out to medically underserved women could be dramatically undermined.
The Johns Hopkins Breast Center continues to promote monthly breast self exams, annual mammograms and annual clinical breast exams for its patients. This remains our best weapon for early detection until other methods such as breast lavage are further developed and become standard practice.
SOURCES:
The Journal of the National Cancer Institute, September 20, 2000; 92:1490-1499
The Susan G. Komen Breast Cancer Foundation (http://www.komen.org)
Western Journal of Medicine, June 2000; 172:379-384
Cancer, August 1, 2000; 89:696-705
American Journal of Epidemiology, September 2000; 152:432-437
"Health, United States: 2000"; Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, GA
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