A new poll shows that women in their 40s want screening mammography despite the The U.S. Preventive Services Task Force recommendation that it not start until age 50. The article gives several reasons for women holding this view; but the real reason is that they have not been educated properly. It’s hard to fault them when most physicians don’t understand the principles of screening for disease and thus are ill equipped to inform their patients.
Many women are said to believe that the Task Force’s recommendations were made to save money. They don’t seem to be aware that there is a down side to screening. The incidence of breast cancer in women without a family history of early onset disease age 39 to 49 is so low that routine mammography likely carries more risk than benefit. As you can see from the data below you have to screen almost 2000 women in this age group to save one life. This means long term breast exposure to radiation which itself may cause breast cancer. It certainly means many unnecessary breast biopsies and all the emotional turmoil that a suspicious mammogram causes. The positive predictive value of positive mammogram is about 5%. This value is the likelihood that the mammogram is positive because of a cancer. In younger women the positive predictive value is doubtless much lower.
The assumption that mammography in this age group saves any life is based on a statistical aberration. Looking at the data analyzed below you can see that none of the studies listed, all of women 39-49, showed a statistically significant benefit in this age group; but when lumped together they were statistically significant. Thus mammography in women age 39-49 may actually save no lives. In the figure below if the line for each study straddles 1 it’s not significant. Remember that meta-analysis is to analysis as metaphysics is to physics.
Women need to be better educated about the value of mammography so they can make better decisions about when to employ it. To that end I have appended the US Task Forces two most recent papers on the subject. While they are not literary gems, a layman can understand their content. If a younger women is at average risk for breast cancer the US Task Force’s recommendations represent the best advice we can currently give about screening for breast cancer, ie, don’t start until age 50.