A group of 29 independent experts from 16 countries, convened by the specialized cancer agency of the United Nations, has concluded that there is sufficient evidence that mammography screening is effective in reducing breast cancer-related deaths for women aged 50–69 years.
The benefit of reduced mortality extends to women screened at age 70–74 years, according to the International Agency for Research on Cancer (IARC), which is part of the UN World Health Organization (WHO).
A summary of the assessment carried out by the group, which considered emerging technologies, clinical breast examination, and breast self-examination, was published yesterday in the New England Journal of Medicine. It provides a critical update to the landmark2002 IARC Handbook on Breast Cancer Screening in light of recent improvements in treatment outcomes for late-stage breast cancer and new data on screening practices and their outcomes.
“Careful consideration of both the benefits and harms of mammography screening shows a net benefit from inviting women 50–69 years old,” Dr. Lauby-Secretan, an IARC scientist and the Responsible Officer for the Handbooks Series, said in a news release.
“The significant reduction in breast cancer mortality observed in this age group outweighs the effects of overdiagnosis and other adverse effects,” she added.
An evaluation of data from studies conducted in high-income countries (in Australia, Europe, and North America) showed that women 50–69 years of age who attended mammography screening had a reduction in breast cancer mortality of around 40 per cent.
“Providing early access to effective diagnosis and treatment in developed and developing countries is critical to reduce breast cancer mortality globally,” said Dr. Christopher Wild, the Director of IARC. “The IARC Handbook on breast cancer screening provides the most up-to-date evaluation of the scientific evidence. This provides a foundation on the basis of which governments can implement the best intervention strategies in order to save more lives.”
However, evidence for the effectiveness of screening women in the younger age group of 40–49 years was considered limited. The most important harms of early detection of breast cancer by mammography screening are false-positive results, overdiagnosis, and radiation-induced breast cancer.
Among the group’s conclusions is that there is sufficient evidence that mammography screening detects breast cancers that would never have been diagnosed or caused harm if the women had not been screened. There is also sufficient evidence of an increased risk of radiation-induced breast cancer from mammography screening in women aged 50 years or older but that risk is substantially outweighed by the reduction in breast cancer mortality.
Evaluation of the current literature also showed that there is sufficient evidence that clinical breast examination is associated with the detection of smaller and earlier-stage tumours. However, no data were yet available for an evaluation of the effect of this screening technique on breast cancer mortality. For breast self-examination, most studies did not show a reduction in breast cancer mortality.
Numerous studies have investigated the beneficial effects of screening modalities other than mammography. However, none of the emerging technologies, either in addition to or as a replacement for mammography, had sufficient evidence of a reduction in breast cancer mortality.
Breast cancer is the most common cause of death from cancer in women worldwide, the second leading cause of death from cancer in women in high-income countries, and the leading cause of death from cancer in low- and middle-income countries, where a high proportion of women present with advanced disease, which has a poor prognosis.
Established risk factors for breast cancer include age, a family or personal history of breast cancer or pre-cancerous lesions, genetic predisposition, reproductive factors, hormonal treatment, alcohol consumption, obesity, and exposure to ionizing radiation.