Tuesday, November 17, 2009

Cost benefit in cancer screening

The U.S. Preventive Services Task Force has issued a stunning recommendation. It recommends against routine screening mammographies for women 40-49 years old with no other risk factors for breast cancer and recommends only biennial mammographies for women 50-74 years old. It also recommends against teaching women how to self-examine.

The recommendations reverse those made by the same group in 2002.

The task force reviewed evidence from numerous studies in making its recommendation.

It concluded that there is a benefit to regular screening mammographies; the evidence demonstrates that they reduce cancer mortality among women aged 40 and over. The benefits increase with age. So, the task force's recommendation will likely contribute to a higher death rate.

However, the task force cited new evidence that the mortality benefits were exceedingly small. For every 1,903 women aged 40-49 who were given the opportunity for annual screening, only one cancer death would be avoided. For women aged 50-59, the ratio was 1,339 to one. The new evidence was largely responsible for the change in recommendations.

The task force balanced this small but undeniable benefit against "moderate" costs and harms from screening.
The harms resulting from screening for breast cancer include psychological harms, unnecessary imaging tests and biopsies in women without cancer, and inconvenience due to false-positive screening results. Furthermore, one must also consider the harms associated with treatment of cancer that would not become clinically apparent during a woman's lifetime (overdiagnosis), as well as the harms of unnecessary earlier treatment of breast cancer that would have become clinically apparent but would not have shortened a woman's life. Radiation exposure (from radiologic tests), although a minor concern, is also a consideration.
The task force found no benefit from self-exams but some of the same harms as mammographies.

An interesting thought experiment is to consider how the recommendations might change yet again if a less expensive but more accurate screening technology is developed (the recommendations do compare film, digital, and MRI screenings). A technology that reduced the screening costs and led to more true positives and fewer false positives could well tip the balance back in favor of additional screenings.

With the current technology, however, the "rational" approach is to cut back on screeings.