Mammography, Breast Cancer and What Women Need to Know
The results of a recent study published in the British Medical Journal may be confusing to women when it comes to the reliability of mammography. According to the study’s authors, Jorgensen and Gotzsche, screening mammogram results lead to an overdiagnosis of breast cancer. In their study, one in three breast cancers detected by organized screening mammography was overdiagnosed.
The term “overdiagnosed” refers to the detection of abnormalities, say, in the breast tissue, that will never cause symptoms or death during a patient’s lifetime. Overdiagnosis of breast cancer or any cancer occurs when the disease grows so slowly that the patient dies of other causes before the cancer ever produces symptoms or it remains dormant.
One problem with overdiagnosis is that because doctors don’t know which patients are overdiagnosed, the tendency is to treat everyone who shows any abnormalities. The result is unnecessary treatment, which can itself cause other health problems.
In the current study, the investigators evaluated data from a fourteen-year period (seven years before and seven years after screening mammography) from women in the United Kingdom, Canada, Australia, Sweden, and Norway. It did not include women from the United States.
One factor that may have an impact on the results of the current study is that the investigators looked at both invasive breast cancers and a type called ductal carcinoma in situ (DCIS), the most common type of noninvasive breast cancer. This type of cancer is noninvasive because it has not spread beyond the milk ducts into any surrounding normal tissue.
According to the American Cancer Society, about 60,000 cases of DCIS are diagnosed in the United States each year. Women who have had DCIS are at greater risk for the cancer coming back or for developing a new breast cancer than women who have never had breast cancer. However, the chances of recurrence are less than 30 percent. By including DCIS in the British Medical Journal study, the estimate of overdiagnosis may be exaggerated, as most cases of DCIS are never expected to become full-blown cancer.
Women should also know that according to a study in the Journal of the National Cancer Institute, 10 percent of mammogram results are false positives, which means the results indicate cancer when there really is no disease there. Women who get a false-positive test result typically return for additional testing. Digital mammography reportedly has a lower false-positive rate, and women may want to insist on this technology when getting a mammogram.
Mammography is and probably will remain a controversial technique for some time. In the United States, women age 40 and older are urged by the American Cancer Society and other health organizations to get a mammogram every one to two years. Women are also encouraged to do breast self-exams once a month. These are personal choices, but the choice is not many any easier by the confusing and sometimes conflicting information provided about the benefits and risks of mammography and the data on breast cancer risks. More research is still needed to help women make informed decisions when it comes to mammography and breast cancer.
American Cancer Society
Elmore JG et al. Journal of the National Cancer Institute 2002 Sept; 94(18): 1373-80.
Jorgensen KJ, Gotzsche PC. British Medical Journal 2009 Jul 9; 339:b2587.