BMJ: Updated model links mammo screening with net harms
The Forrest report led to the introduction of screening mammography in the U.K. It estimated the number of screened and unscreened women surviving each year over a 15-year period. Costs and benefits were measured in QALYs, but the report omitted harms. The original report suggested that screening would reduce the death rate from breast cancer by almost one-third with few harms and at low cost.
The current study updated the original by including harms. Specifically, James Raftery, PhD, professor of health technology assessment at Wessex Institute in Southampton, U.K., and Maria Chorozoglou, researcher fellow at the institute, incorporated false positives and overtreatment.
“Assessment of the effects of mammographic breast screening in terms of mortality or life years inevitably shows positive benefits because of the omission of harms,” wrote Raftery and Chorozoglou.
The researchers combined the benefits and harms of screening in one single measure and based the study on 100,000 women, ages 50 and older, surviving by year up to 20 years after entry to the screening program. Women were divided into screened and unscreened cohorts and the outcome measures included deaths from breast cancer, deaths from all other causes and the number of women with false-positive diagnoses and surgery, which were combined into QALYs.
Inclusion of false positives and unnecessary surgery reduced the benefits of screening by about half, according to Raftery et al. The researchers produced five scenarios based on multiple trials that analyzed mortality, quality of life and false positive diagnoses. The best estimates generated negative net QALYs for up to eight years after screening and minimal gains after 10 years.
After 20 years, net QALYs accumulate, but by much less than predicted by the Forrest report, according to the researchers.
“Ways of reducing the harms from screening might include less frequent screens, particularly for younger women. While further modeling might explore the clinical and cost effectiveness of various options, conclusions will inevitably be limited without better estimates of the level and impact of overtreatment,” they wrote.
The researchers noted that the current analysis offered a single loss of quality of life to surgery whether it was mastectomy or lumpectomy and did not include harms of radiotherapy and chemotherapy.
Raftery and Chorozoglou suggested that future studies of breast cancer screening include the harms and also advised that physicians communicate the meaning and implications of overdiagnosis and overtreatment to patients.