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UICC World Cancer Congress 2006
Bridging the Gap: Transforming Knowledge into Action
July 8-12, 2006, Washington, DC, USA
Early diagnosis is obtained through education, both of the target population and health care professionals, especially at the primary care level. Education programs should be culturally sensitive, designed, especially in many developing countries, to dispel myths that breast cancer is an incurable, inevitably fatal disease. Education of primary care practitioners in all countries should facilitate their recognition of the signs of early breast cancer, which are often subtle, very different from the signs of advanced breast cancer usually taught, even in developed countries. Education programs should precede the introduction of screening programs, and should be an integral part of such programs.
The screening tests used for breast cancer include mammography, physical examination of the breasts (screening clinical breast examination) and breast self examination. The 2002 IARC review concluded that there was sufficient evidence that mammography alone in women age 50-69 reduced mortality from breast cancer. This was based on several randomized trials of screening, the majority being conducted in Sweden before adjuvant chemotherapy and tamoxifen became normal usage. In contrast, the Canadian National Breast Screening Study 2 (CNBSS 2) failed to find any reduction in breast cancer mortality from adding mammography to breast physical examinations and the teaching of Breast Self Examination (BSE) in women age 50-59, the trial being conducted when adjuvant chemotherapy and tamoxifen were generally applied in Canada for women with Stage 2 disease. That the difference between the Swedish and Canadian trials in adjuvant treatment had an impact is seen by the major difference in 13-year survival for cases detected by the physical examination arm of the CNBSS 2 (83%) and the control arm of the Swedish Two county trial (75%), whereas the survival for cases detected in the mammography containing arms of both trials was identical (83%).
The IARC (2002) review concluded that the evidence for the effectiveness of mammography screening in women age 40-49 was limited. This was because a meta-analysis failed to find a significant reduction in breast cancer mortality. Preliminary results in the UK trial of women recruited at ages 40-41 suggested a similar lack of significant benefit. This is a major problem for many developed countries where, because of their population pyramids, breast cancer is relatively more frequent in women age 40-49.
It has been assumed by many that mammography screening is having a major impact upon breast cancer mortality in several developed countries, yet the reduction in breast cancer mortality that has occurred in Canada, the United Kingdom and the United States began too soon to be explained on the basis of mammography screening, but seems explicable on improved treatment. In this respect, a recent model analysis has over-estimated the benefit derived from screening in the United States, largely because it regarded the benefit from screening and from adjuvant treatment as additive, which resulted in having to make an assumption that in the absence of improved treatment and screening, mortality in the US would have risen, an assumption not compatible with stable mortality since the 1970s until 1990.
The first breast screening trial was conducted in New York in the 1960s, when mammography was in an early stage of development, and adjuvant therapy was not available. The significant benefit found was probably largely due to the breast physical examinations. CNBSS 2 demonstrated that mammography results in the diagnosis of in situ carcinomas and good prognosis small invasive cancers that do not impact upon breast cancer mortality, providing a woman is having regular good breast physical examinations. This indirect indication of the value of breast physical examinations was re-enforced by a model based evaluation of CNBSS 2, that suggested that the examinations resulted in a 20% reduction in breast cancer mortality. However, we do not have level 1 evidence to support the implementation of population-based screening breast physical examinations, and research into its effectiveness has high priority. Such screening, with mammography and ultrasound reserved for diagnosis, is now being evaluated in India and Egypt, and potentially in other countries in the Middle East. There is preliminary indication from the Egyptian trial that stage shift towards more limited disease is being achieved by screening. If the results from these trials eventually show that breast cancer mortality can be reduced by such approaches, it is likely to be expanded to many Middle Income countries that cannot afford mammography screening. In the meantime, countries with an important breast cancer problem should concentrate on early diagnosis through health promotion and the provision of adequate treatment for detected cases.
In technically advanced countries, the hope resides in new screening tests, preferably ones that would detect the true precursors of breast cancer. In the meantime, there is little evidence that improvements in mammography are being translated into reduced breast cancer mortality. As treatment improves with the introduction of new agents, the role of mammography screening may diminish further.