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In Reply We agree with Dr Moy that multiple randomized clinical trials and meta-analyses suggest that mammography leads to a statistically significant decrease in breast cancer mortality of approximately 19%.1 Nevertheless, these screening trials were conducted decades ago (starting in the 1960s), and since then both mammography technology and breast cancer treatment have improved substantially, raising questions as to whether the randomized clinical trial data may underestimate or overestimate the real benefit of mammography in today’s context, a point emphasized in the systematic review accompanying the ACS guideline.2 And although, as Moy notes, more recent observational studies suggest mortality reductions of up to 48% for women older than 40 years who are actually screened, such observational studies are limited by potentially noncomparable control groups (because screening participants are typically healthier than others), lead-time and length-time bias, and challenges differentiating benefits of screening from improvements in breast cancer diagnosis and treatments over time. Although we do believe that the evidence supports a likely mortality benefit from mammography, we believe it is most likely modest and almost certainly lower than that suggested by observational studies.
Keating NL, Pace LE. Screening Mammography and Age Recommendations—Reply. JAMA. 2016;315(13):1405. doi:10.1001/jama.2015.19090