The study touts a larger benefit than was found by earlier studies, which recently led an influential panel of U.S. science advisers to recommend against routine screening before age 50. The panel said the benefits were so small and potential problems from screening so great that the decision should be left to each woman and her doctor. And just last week, another study in Norway found that the benefit of mammograms even for women 50 and older is less than has been believed.
The new study has major limitations, and cannot account for possibly big differences in the groups of women it compares. Nor does it consider the harm — such as unnecessary stress, unwarranted biopsies and overtreatment — of screening women in their 40s. Breast cancer is less common in that age group, so mammograms can raise many false alarms.
A spokeswoman for the American Society of Clincal Oncology (ASCO) said "it captures the real-world experience" they have from regular mammograms, said Dr. Jennifer Obel.
"It's just one piece of evidence supporting the fact that screening women in their 40s does save lives," said the ASCO's chief medical officer, Dr. Otis Brawley. "We believe that women in their 40s should be screened, but we also believe that women should be informed of the limitations of mammography."
Critical to the integrity of statements and research from ASCO is the absence of bias in the process. Ironically ASCO strongly recommends the elimination of conflicts of interests, whether they are actual or potential, yet they are directly funded by pharmaceutical and other industry sources either directly or indirectly.
The Swedish researchers estimate that 1,252 women in their 40s would have to be offered screening every other year for 10 years to save one life.
Results of the new study were reported in a teleconference yesterday and will be presented at a cancer conference in Washington later this week. They also were published online by the journal Cancer.
The U.S. Preventive Services Task Force's panel last fall recommended against routine screening for women in their 40s. Thousands of scientists and medical professionals are unconvinced from conclusions of the new study and maintain that extreme caution is necessary before recommending a mammogram at any age.
Dr. Jeanne Mandelblatt, a Georgetown doctor who headed six research teams for the government panel, said the new study "does not balance the benefits against the harms," as the panel sought to do.
The new study looked at Sweden's mammography program. Since 1986, the country has required that screening be offered to women over 50 but left it up to each county to decide whether to offer it to younger women. About half of counties did, and researchers compared breast cancer death rates in areas where it was and wasn't offered.
They counted breast cancer deaths of women who had been diagnosed in their 40s and died within 16 years of followup. They compared two groups, one where screening was available and one where it was not.
The number of women in each group studied and the amount of time they were followed differed. Researchers did not express the results in terms of death rates, which would have made comparing these groups much easier.
Researchers did not have information on, and the study therefore could not account for, any differences in general health and other factors that could have affected the number of deaths.
"This is a very unscientific study based on findings and conclusions which completely ignore the potential risks and dangers associated with mammorgrams," said Dr. Kimberely Schor, a panelist who examines medical research.
Mammograms are frequently misread by doctors which have spurred lawsuits in every state in the last twenty years. Before pursuing a mammogram, consider the following:
A routine mammogram screening typically involves four x-rays, two per breast. This amounts to more than 150 times the amount of radiation that is used for a single chest x-ray. Bottom line: screening mammograms send a strong dose of ionizing radiation through your tissues. Any dose of ionzing radiation is capable of contributing to cancer and heart disease.
Screening mammograms increase the risk of developing cancer in premenopausal women.
Screening mammograms require breast tissue to be squeezed firmly between two plates. This compressive force can damage small blood vessels which can result in existing cancerous cells spreading to other areas of the body.
Cancers that exist in pre-menopausal women with dense breast tissue and in postmenopausal women on estrogen replacement therapy are commonly undetected by screening mammograms.
For women who have a family history of breast cancer and early onset of menstruation, the risk of being diagnosed with breast cancer with screening mammograms when no cancer actually exists can be as high as 100 percent.
A large-scale screening study published in September of 2000 by epidemiologists at the University of Toronto revealed that monthly breast self-examination following brief training, coupled with an annual clinical breast examination by a trained health care professional, is at least as effective as mammography in detecting early tumors, and also safe.
Since we know that properly performed breast exams are just as effective at detecting early tumors as mammography, how can we justify the use of screening mammograms when we know that all forms of ionizing radiation increase the risk of developing cancer and heart disease?
Per-Henrik Zahl, M.D., Ph.D., of the Norwegian Institute of Public Health, Oslo, and his research team studied breast cancer rates among 119,472 women (age 50 to 64). These research subjects were asked to participate in three rounds of screening mammograms between 1996 and 2001, as part of the Norwegian Breast Cancer Screening Program. The scientists then compared the number of breast cancers found in this group to the rate of malignancies among a control group of 109,784 women who were the same ages in 1992, and who would have been invited for breast screenings if the program had been in place that year. Cancers were tracked using a national registry. Then, after six years, all participants were invited to undergo a one-time screening to assess for the prevalence of breast cancer.
The researchers were surprised to find that the incidence of invasive breast cancer was 22 percent higher in the group regularly screened with mammography. In fact, screened women were more likely to have breast cancer at every age.
"Because the cumulative incidence among controls never reached that of the screened group, it appears that some breast cancers detected by repeated mammographic screening would not persist to be detectable by a single mammogram at the end of six years," the authors stated in their report. "This raises the possibility that the natural course of some screen-detected invasive breast cancers is to spontaneously regress."
The researchers also conclude that their findings "provide new insight on what is arguably the major harm associated with mammographic screening, namely, the detection and treatment of cancers that would otherwise regress."
Marco Torres is a research specialist, writer and consumer advocate for healthy lifestyles. He holds degrees in Public Health and Environmental Science and is a professional speaker on topics such as disease prevention, environmental toxins and health policy.