The appropriateness of mammography screening has long been an issue in the medical community, especially in light of the US Preventive Services Task Force 2009 recommendation against routine mammography screening for women between the ages of 40 and 49 (you can read more of our coverage on the topic here
). With a pair of articles by Kopans et al
and Jorgensen et al
, the September issue of Radiology
continues the debate on the effectiveness of mammography screening in preventing breast cancer mortality and the risk of overdiagnosis.
The key concern when analyzing the appropriateness of mammography screening is that, in Jorgensen’s words, “the goal of screening mammography is earlier detection of only those invasive tumors that would otherwise be lethal.” An unknown percentage of breast cancers, especially ductal carcinoma in situ (DCIS), can remain noninvasive and would never become clinically evident. Though highly contentious, some researchers even suggest that detectable breast cancer can spontaneously regress if left untreated. The authors of both articles disagree about appropriate estimates for these cases of overdiagnosis, with estimates ranging anywhere from 1% or 2% (the low end of Kopans’ estimates) up to 57% (the high end of Jorgensen’s estimates).
Although the extent of overdiagnosis is unknown, overtreatment of breast cancer can be harmful, including not just psychological damage but also exposure to radiation and unnecessary mastectomies. Jorgensen et al suggest that as clinical treatment of breast cancer improves alongside increased public awareness, mammography screening is no longer as important in preventing breast cancer mortality. If screening is successful in detecting earlier stages of breast cancer, then the increase in incidence of DCIS and early stages of breast cancer should be offset by a reduction in rates of invasive breast cancers. But according to data found by Jorgensen, there has not been a significant decline in invasive breast cancers.
However, recent estimates from the Swedish Two-County Trial indicate that screening is effective in lowering the breast cancer mortality rate. In the study, 133,065 women between the ages of 40 and 74 were randomized into a control group and a study group who were routinely screened for breast cancer. Ten years after the randomization period, results showed that 71 deaths had been prevented. But 29 years after the randomization period, 158 deaths had been prevented. In other words, most of the deaths prevented by the screening only became apparent more than ten years past the randomization period.
This finding suggests that the most accurate data about mammography screening may only come to light with more long-term research studies. We may not have definitive data on the benefits of screening and the extent of overdiagnosis for quite some time. This lingering debate might even help explain the recent decline in mammography screening. Our research found a 1.5% decline in mammography screening between 2009 and 2010 volumes, a marked departure from the 3.6% growth between 2008 and 2009. For more on mammography volumes and market trends, see our 2011 Imaging Growth Survey.