Of women who get yearly mammograms, 61 percent will have at least one false-positive result over a decade, a new study shows.
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.
In a Swedish study of 60,000 women, 70 percent of the mammographically detected tumors weren't tumors at all. These "false positives" aren't just financial and emotional strains, they may also lead to many unnecessary and invasive biopsies. In fact, 70 to 80 percent of all positive mammograms do not, upon biopsy, show any presence of cancer.
At the same time, mammograms also have a high rate of missed tumors, or "false negatives." Dr. Samuel S. Epstein, in his book, The Politics Of Cancer, claims that in women ages 40 to 49, one in four instances of cancer is missed at each mammography. The National Cancer Institute (NCI) puts the false negative rate even higher at 40 percent among women ages 40-49. National Institutes of Health spokespeople also admit that mammograms miss 10 percent of malignant tumors in women over 50. Researchers have found that breast tissue is denser among younger women, making it difficult to detect tumors. For this reason, false negatives are twice as likely to occur in premenopausal mammograms.
And because of these 'false alarm' test results -- which seem to indicate cancer but further tests reveal not to be tumors --7 to 9 percent of women will be recommended to get a biopsy.
If women are instead screened every other year, only 42 percent will have a false positive over a decade, but this lengthened screening interval brings a small increased risk of getting a later-stage cancer diagnosis, the study showed.
"We hope that by helping women know what to expect in terms of false-positive results, they'll be less likely to experience anxiety when they are called back for a repeat screening or biopsy," said study researcher Rebecca Hubbard, an assistant investigator at the Group Health Center for Health Studies in Seattle.
The study researchers say they recommend that women and their doctors develop a screening plan based on the patient's individual risk factors for breast cancer and her tolerance for dealing with such false alarms.
The study will be published online tomorrow (Oct. 18) in the journal Annals of Internal Medicine.
The topic of how often women should get mammograms and at what age they should start has been controversial. The American Cancer Society recommends all women with average risk of breast cancer get a yearly mammogram starting at age 40, and the National Cancer Institute recommends women age 40 and older get a mammogram every year or two.
On the other hand, the U.S. Preventive Services Task Force issued new recommendations in 2009 that women should wait until age 50 to begin the screening, and should have a mammogram every other year, citing false detections, and the unnecessary biopsies and anxiety they can bring.
The new findings emphasized the importance of radiologists being able to review a patient's previous mammograms because it "may halve the odds of a false-positive recall,'' the researchers wrote. Though recommendations for for further testing -- fine-needle aspiration or surgical biopsy -- are less common than false positives, they can lead to unnecessary pain and scarring. The additional testing also contributes to rising medical costs.
"We conducted these studies to help women understand that having a false-positive result is part of the process for mammography screening," Hubbard said.
The researchers used data from seven mammography registries in the Breast Cancer Surveillance Consortium, a comprehensive breast cancer registry. They looked at data from nearly 170,000 women from seven regions around the United States, and almost 4,500 women with invasive breast cancer.
Mammograms are going digital
A second study compared digital mammograms with the older technology, film mammograms. Digital mammograms are increasingly being used, the researchers said.
That study included data nearly 330,000 women between the ages of 40 and 79, also from the Breast Cancer Surveillance Consortium.
The researchers found that digital and film mammography were equally effective for women over age 50, but for women ages 40 to 49 -- especially those with dense breast tissue -- digital mammograms were slightly more likely to find a cancer. However there was also an increased risk for false positive results for these younger women.
The researchers found that for every 10,000 women 40 to 49 who are given digital mammograms, two more cases of cancer will be identified for every 170 additional false-positive examinations.