Researchers from Denmark have reported that one-third of women may be unnecessarily treated for breast cancer as a result of public screening programs that over-diagnose the disease. The results of this study appeared in an early online publication in the British Medical Journal on July 9, 2009.[1]

Breast cancer is the second leading cause of cancer death in women in the United States, with approximately 180,000 cases diagnosed each year. The best “treatment” for cancer is to prevent its occurrence or to detect it early when it is most treatable. As a result, screening for breast cancer has become standard for women over 40 as well as women who are at high risk of developing the disease.

In theory, the number of cases of advanced breast cancer should drop after the initiation of large-scale public screening programs; however, data to document this is confusing to say the least. Some researchers have speculated that large screening efforts may actually lead to over-diagnosis of breast cancer. However, most researchers would admit that current screening techniques do not adequately distinguish between a breast cancer that requires treatment and one that does not.

Researchers from Copenhagen analyzed breast cancer trends in the years before and after the initiation of government-run mammography screening programs in Australia, the United Kingdom, Canada, Sweden, and Norway. The data covered a period of at least seven years prior to screening and seven years after screening had been implemented.

The results indicated that one in three women who were identified as having breast cancer did not actually need to be treated. Some cancers grow too slowly to affect the patient. Because cancer treatment often causes harmful side effects and can be physically and emotionally stressful for patients, not all patients benefit from undergoing treatment.

These researchers concluded that “the increased incidence of breast cancer was closely related to the introduction of screening.”

Comments: The validity of this kind of analysis rests on the reliability of incidence data before and after screening mammography was instituted in various countries. Despite the findings it is difficult to believe that a screening procedure, such as mammography, which only detects 30-40% of all early-stage breast cancers can have such a major impact in detecting cancers that are not destined to kill the patient if undiagnosed. There is emerging data from many separate studies that early detection by mammography and other screening techniques results in earlier diagnosis and fewer patients having advanced disease. What is currently needed is a better screening tool for detecting early breast cancer. However, it has to be conceded that in order to improve survival in women with breast cancer, some women will be treated unnecessarily. What is in question is the fraction of “over-diagnosed” cases in relation to the total number detected. One third seems a very high number and does not correlate with other studies. One Danish study, for instance, did not find “over diagnosis” to be a problem in a screened population of women.

Reference:

[1] Jorgensen KJ, Gotzche PC. Overdiagnosis in publicly organized mammography screening programmes: Systematic review of incidence trends. British Medical Journal [early online publication]. July 9, 2009. DOI:10.1136/bmj.b2587.