Tuesday, December 20, 2011

Screening mammography decisions are close calls

A physician reader of AFP submitted the following post.


I read with interest the December 1st Cochrane for Clinicians article by Dr. Joanne Wilkinson, "Effect of Mammography on Breast Cancer Mortality." On the first page of the article in big print is the "Evidence-Based Answer," which gives a SORT "A" recommendation in favor of mammography because of an approximate 15% reduction in mortality from breast cancer attributed to mammography screening. In small print inside are the conclusions from the Cochrane abstract, which note a 30% rate of overdiagnosis and overtreatment. The Cochrane authors write:

This means that for every 2,000 women invited for screening over 10 years, one will have her life prolonged, and 10 healthy women who would not have been diagnosed if there had not been screening will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false-positive findings. It is not clear whether screening does more good than harm.

Having read this - I wonder how many women would continue to opt for regular mammography screening if told that only 1 out of every 2,000 will benefit, whereas 10 out of 2,000 will be overtreated (some presumably with mastectomy), and 200 out of 2,000 (10%) will be temporarily overdiagnosed (and subject to important psychological distress for many months) because of a false-positive mammography reading. Given these statistics, observers outside of the medical community might wonder why "primary care physicians should continue to recommend mammography every two years in women 50 to 74 years of age," as the last paragraph of Dr. Wilkinson's commentary states.

As in much that the primary care clinician does, there are pros and cons to any intervention. For patients to give truly informed consent, it is essential for us to convey to them the numerical chance for life-prolonging benefit (1 in 2,000 for women who undergo yearly mammography for a decade) versus the 1 in 10 risk of a falsely positive mammogram report, and the 1 in 200 risk of overtreatment during that 10-year period. For some women who subscribe to the "n of 1" theory, screening mammography may be worth the risk, effort and cost because of the chance that it may save their lives. Others may decide that the odds of experiencing benefit are not in their favor. Shouldn't the choice to undergo mammography be up to the patient?

Ken Grauer, MD
Gainesville, Florida