Benefits, Limitations and Methodology of Population Screening For Breast Cancer
Benefits, Limitations and Methodology of Population Screening for Breast Cancer
Whether breast cancer screening does more harm than good has been debated extensively. The main questions are how large the benefit of screening is in terms of reduced breast cancer mortality and how substantial the harm is in terms of over diagnosis, which is defined as cancers detected at screening that would not have otherwise become clinically apparent in the woman's lifetime(Chen et al. , 2013, pp. 1043-50 ). The debate about the benefits and harms of breast screening is not unique to the US and its breast cancer screening programs. . In 2009, the US Preventive Services Task Force re-examined the efficacy of various screening modalities. They recommended that women younger than 50 years do not need to be screened routinely and women aged 50-74 years should have biennial rather than annual screens. The Canadian Taskforce on Preventative Health Care updated their guidelines for breast screening in 2011, and concluded that the reduction in mortality associated with screening mammography is small for women aged 40-74 years at average risk of breast cancer (Evans, 2012, pp. 348-52). They also noted a greater reduction in mortality for women 50 years and older than for those younger than 50 years, and that the risk of over diagnosis and biopsy might be greater for younger than for older women. They recommended that women aged 50-74 years be screened routinely, but stated that substantial uncertainty exists around the evidence for this recommendation. The Cochrane Review concluded that, despite their substantial methodological limitations, trials showed that screening reduced breast cancer mortality, but at the cost of substantial harm from over diagnosis
Measurement of benefit
The aim of screening is to advance the time of diagnosis so that prognosis can be improved by earlier intervention. Earlier diagnosis leads to an increase in the apparent incidence of breast cancer and extends the time between diagnosis and death, even if screening does not confer any benefit(Groenewoud, 2012, pp. 211-8). The appropriate measure of benefit, therefore, is the reduction in mortality from breast cancer in women offered screening compared with those who are not.
Randomized controlled trials
Randomized controlled trials potentially provide the most reliable information about the effects of breast screening. High-quality randomized controlled trials are prone to fewer distorting effects, or biases, than are observational studies. For this reason, the Panel's quantitative estimate of the benefits of breast screening is based on randomized trials of breast screening(Kuhl et al. 2013, pp. 8469-76). A specific issue raised by some commentators is that most of the randomized trials of breast screening date from the 1980s or earlier. Since then, treatment and management of breast cancer have improved, and changes in the incidence of breast cancer and in mammographic techniques have occurred. Are the trials still relevant? Such a question can be asked of any area of medical investigation or treatment, because trials refer to the past and our use of interventions ...