Balance sheet shows benefits of mammo screening outweigh harm

The lives saved by population-based mammography screening outweigh the harms caused by overdiagnosis, according to a review of breast cancer screening services in Europe published Sept. 13 in a special supplement of The Journal of Medical Screening. The review showed that for every 1,000 women screened every two years from the age of 50 to the age of about 68-69 years, between seven and nine lives would be saved, and four cases of breast cancer would be overdiagnosed.

The European Screening Network (EUROSCREEN) working group, with members from nine European countries where outcome of screening programs have been assessed, reviewed the estimates of benefit in published European studies in terms of breast cancer deaths prevented, and the major harms, focusing on overdiagnosed cancers.

A second working group–European Network for Indicators on Cancer (EUNICE)–reviewed the organization, participation rates and main performance parameters of 26 screening programs in 18 countries, involving 12 million women, between 2001 and 2007. The reports from both working groups contributed to the review.

Stephen W. Duffy, MSc, professor of cancer screening at Queen Mary, University of London and coordinator of the EUROSCREEN working group, said in a press release: "This is the only comprehensive review of the results of breast screening services in Europe. It reports results from screening millions of women, and confirms that the screening services are delivering the benefits expected from the research studies conducted years ago. In particular, it is good news that lives saved by screening outweigh over-diagnosed cases by a factor of two to one."

The researchers also found that for every 1,000 women screened, 170 women would have at least one recall followed by a non-invasive assessment before absence of cancer could be confirmed, and 30 women would have at least one recall followed by invasive procedures, such as a biopsy, before confirming a negative result.

Eugenio Paci, MD, director of the Cancer Prevention and Research Institute in Florence, Italy, a EUROSCREEN coordinator, and colleagues emphasized the long-term nature of breast cancer screening programs and explained that analysis of final outcomes of screening programs requires a minimum of 20 years of follow-up.

The researchers explored potential impacts of other evolutions in screening, conceding that digital mammography might be more sensitive to early cancers and ductal carcinoma in situ [DCIS], which could decrease mortality and also increase overdiagnosis. However, improved training and quality assurance could shift the balance in favor of benefits. In addition, they wrote, “There is some evidence that screen-detected DCIS is a progressive disease with a high likelihood of progression to invasive cancer in a large proportion of cases.”

The authors recommended additional studies focused on biomarkers of tumor aggressiveness as well as development of protocols for patient communication, treatment and follow-up of cancers that have low-life threatening potential. They also stressed the need to improve screening specificity and called for research in breast imaging technology.