MONDAY, Sept. 2, 2002 (HealthDayNews) -- In findings that will no doubt revive the heated debate over mammography, Canadian researchers have found women in their 40s who had annual mammograms over five years did not have a lower mortality rate than women who were not screened.
This eagerly anticipated third report from the Canadian National Breast Cancer Screening Study tracked the women for 13 years. Two earlier reports, at seven and 10 years, had similar results. The latest research appears in tomorrow's issue of the Annals of Internal Medicine.
"Mammography did not reduce mortality in the 40-to-49 age group," says Dr. Cornelia Baines, co-principal investigator of the study and professor emeritus in the department of public health sciences at the University of Toronto. "It's important to realize that much of what we believed until recently has been fueled by wishful thinking. The evidence has never been there to warrant the enthusiasm with which screening is taken up. There isn't evidence supporting effectiveness of screening in this age group."
This unwelcome news comes on the heels of several other studies with similar results.
Ironically, Baines says, "mammography did achieve early detection. It found more cancers. It found smaller cancers with less nodal follow-up." Nevertheless, after 13 years of follow-up, the number of deaths were the same for both groups of women.
The Canadian study followed 50,430 women who were between 40 and 49 years of age when they were first enrolled in the study. Participants were randomized into one of two groups: one that received annual mammograms along with physical breast exams and one that received a single physical breast exam followed by "usual care" from their personal doctor.
Both groups received instruction in how to conduct a breast self-exam. By the end of 1996, 16 years after the first woman was enrolled, 105 women in the mammography group and 108 in the other group had died from breast cancer. A total of 592 cases of invasive breast cancer and 71 cases of in situ breast cancer (in the breast only) were diagnosed in the mammography group, compared with 552 and 29 cases, respectively, in the "usual-care" group.
In the same issue of the journal, the U.S. Preventive Services Task Force (USPSTF) recommends that all women aged 40 and over have mammographies with or without clinical breast exams by a doctor every one to two years. The recommendation was issued after conducting a meta-analysis of eight randomized, controlled trials that provided "fair" evidence, the task force says. The USPSTF also admits the evidence for mammography is strongest in the 50-to-69 age group.
It's not entirely clear why the discrepancy exists, but it does and that will undoubtedly fuel the controversy.
"The whole debate will continue to be in the spotlight," says Dr. Dana Smetherman, co-section head of breast imaging at the Lieselotte Tansey Breast Center at the Ochsner Clinic Foundation in New Orleans. "Mortality has been steadily decreasing in this country, and we have to be doing something right. I think at this point no one wants to completely abandon mammography. It's always going to be a more difficult issue to prove in the younger age group where the incidence is smaller."
Baines disagrees. A number of factors may explain why overall breast cancer mortality is down, including better treatment and the fact that tumors that are brought to medical attention today are much smaller than in the past. "There's a huge difference in size of presentation, and that in itself will demonstrate that even the early detection that we now achieve is enormously better than the very late detection in the first half of the 20th century," Baines says.
For those who say mammography can't hurt, Baines has these sobering remarks: A woman has a one in three chance of getting a false negative response from a mammogram. She has a 50 percent chance of having a false positive if she is between the ages of 40 and 49 and gets screened every year. Seven of every 100 women who are screened will not actually have cancer but will receive treatment anyway. Sixty percent of women would have been cured without the mammogram.
Moreover, Baines says, repeated studies have shown that, since the early 1980s, during the first few years after a screening program is started anywhere, more women die of breast cancer in the mammography group than in the control group. "It's a phenomenon that has been censored both by public and health professionals defending screening," Baines says.
Why do these women die? No one knows, but a "reasonable hypothesis" is that some women may have primary tumors that put out a negative growth factor, suppressing early micrometastases. If this is the case, removing the primary tumors means the tiny metastases are free to flourish.
Mammography does seem to lower mortality in the 50-and-over age group.
So what's a woman -- especially a woman under the age of 50 -- to do? "Breast awareness," Baines says. "Women see their breasts when they have showers, when they're getting dressed and as far as I'm concerned they should do what I did when I was in my 40s: Be aware of changes and be aware of symmetry." Don't worry if one breast is bigger than the other, but do worry if one part of your breast becomes thicker, or looks more full than it did two or three months before, and particularly when the changes are only on one side.
"The tragic story is when a woman finds a lump in her 30s, gets a mammogram and the doctor tells her not to worry about it," Baines says. "If it's an asymmetric lump, you get it biopsied."
What To Do
The Susan G. Komen Breast Cancer Foundation has a wealth of information on all aspects of the disease, as does the National Cancer Institute.
