There is a large body of evidence that mammography screening saves lives. In the mid 1980’s there was a dramatic increase in the number of American women screened. 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.
Yet, a report in the July 28 British Medical Journal claims there is no evidence that mammography screening served a direct role in reducing breast cancer deaths in European countries where screening has been implemented. The authors compared breast cancer mortality trends in three pairs of adjacent countries (Sweden vs. Norway; Northern Ireland vs. Republic of Ireland; and Belgium vs. Netherlands). Each comparison included a country that introduced mammography screening some years earlier than the other. Comparing breast cancer death rates from 1989-2006, the authors observed similar trends in breast cancer death reduction in each pair. They claim mortality trends are more likely influenced by therapy improvements than mammography screening.
The conclusions of the BMJ study authors have little bearing on, or resemblance to, screening in the United States. 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. This is the life-saving effect that the authors of the BMJ 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 in BMJ failed to do so:
1. The mortality data are contaminated with deaths attributable to breast cancer diagnoses that occurred before screening was introduced. During the period 1986-1996 (and thus, also 1993-2003) 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.
2. 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.
3. While Sweden began introducing screening in 1986, not all counties 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 1992-1993.
4. Not all women who develop breast cancer have been invited to screening. Not all those invited to screening attend screening.
5. 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 40 or over increase their risk of dying from breast cancer by not getting annual mammograms. Mammography also provides opportunity for a wider range of treatment options, and increases odds that less aggressive treatment can be successful. This not only save lives, but quality of life as well.
The American College of Radiology and Society of Breast Imaging 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 doctor about being screened even earlier.
For more information regarding the importance of annual mammograms, to receive an annual reminder to get a mammogram or to find an accredited mammography facility, visit www.MammographySavesLives.org.