The American College of Radiology (ACR) and the Society of Breast Imaging (SBI) have issued a statement in response to the controversial study published July 28 in the British Medical Journal (BMJ), which claimed there is no evidence that mammography screening served a direct role in reducing breast cancer deaths in European countries where screening has been implemented.
There is a large body of evidence that mammography screening saves lives, the organizations noted. In the mid 1980s, there was a dramatic increase in the number women screened in the U.S. The sudden increase in breast cancer incidence seen in national statistics was followed by an abrupt decrease in deaths that began five to seven years later. This decrease in deaths in conjunction with the onset of screening confirms the favorable results of randomized trials, case-control studies and large population-based evaluations of mammography screening, according to ACR and SBI.
In the BMJ study, the authors compared breast cancer mortality trends in three pairs of adjacent countries (Sweden versus Norway; Northern Ireland versus Republic of Ireland; and Belgium versus Netherlands). Each comparison included a country that introduced mammography screening some years earlier than the other.
Comparing breast cancer death rates from 1989 to 2006, the authors observed similar trends in breast cancer death reduction in each pair and claimed mortality trends are more likely influenced by therapy improvements than mammography screening.
The BMJ authors’ conclusions have little bearing on, or resemblance to, screening in the U.S., the joint statement maintained. Improvements in therapy have, likely, played a role in the decrease in breast cancer deaths, but therapy cannot cure advanced cancers.
Early detection via mammography is clearly the major reason for the decrease in deaths in the U.S., wrote the ACR and SBI, and this is the life-saving effect that the authors of the study expected to see in Europe (as was seen in cervical cancer screening).
While one may intuitively expect to see more dramatic differences in breast cancer death rate declines—based on timing of mammography introduction in Europe—there are several reasons why the analysis published failed to do so, according to the organizations:
- The mortality data are contaminated with deaths attributable to breast cancer diagnoses that occurred before screening was introduced. During the period 1986 to 1996 (and thus, also 1993 to 2003) half of the breast cancer deaths are attributable to a diagnosis before screening was even offered, much less fully implemented. That leaves insufficient time to measure a population wide effect.
- Just because two nations share similar geography, does not mean their breast cancer mortality trends are easily compared. Compared with Norway, Sweden had roughly 10 percent greater breast cancer incidence during the study period. It was even greater before the study period began. That would influence mortality rates over time—as mortality rates are a function of incidence rates over time and their corresponding survival. The authors did not adjust for incidence rate differences between comparison nations.
- While Sweden began introducing screening in 1986, not all countries did so that year. Not all women received a mammogram in 1986. It takes time to invite the population to screening. Full implementation didn't occur until 1992 to 1993.
- Not all women who develop breast cancer have been invited to screening. Not all those invited to screening attend screening.
- The study did not demonstrate how effectively mammography is functioning in comparison countries. The effectiveness of mammography on a population-wide basis is influenced by the attendance rate and the accuracy of the screening.
Women age 40 or over increase their risk of dying from breast cancer by not getting annual mammograms, the statement added. Mammography also provides opportunity for a wider range of treatment options, and increases odds that less aggressive treatment can be successful, which not only save lives, but quality of life as well, the organizations contended.
The ACR and SBI continue to recommend that women get annual mammograms starting at age 40. Those with a family history of breast cancer (or other factors that place them at elevated risk for the disease) should speak with their physicians about being screened even earlier, the societies added.