Effectiveness: New follow-up results from randomised studies show that mammography screening reduces breast cancer deaths, but the impact is smaller than estimated five years ago. The results indicate that, in the over-50 age group, mortality from breast cancer is some 22% (minimum 13% and maximum 30%) lower in women invited for screening than in those not invited.
The impact that the screening of women aged 60-69 has on the results cannot be reliably identified. Compared with the 50-59 age group, screening is slightly more sensitive in the 60-69 age group (a greater proportion of cancers are detected), that is, cancers are more likely to be detected in the older age group. Furthermore, compared with other age groups currently screened in Finland, screening in the over-60 age group raises less suspicions of cancer that turn out to be false.
Between 1999 and 2003, the age-adjusted breast cancer mortality in Finland was 28.8 per 100,000 women; in the 50-79 age group, it varied between 43 and 106/100,000. Assuming the average mortality for these age groups to be 75/100,000, breast cancer screening by mammography can annually prevent some 16.5 breast cancer deaths per 100,000 women screened (22% of the average of 75 deaths). In other words; breast cancer screening can annually prevent one breast cancer death per 6060 women screened. The impact of screening is here assumed to continue for ten years after screening. Improved methods of treating breast cancer also decrease mortality. It is difficult to distinguish between the independent effects of screening and treatment, which have been estimated to be approximately equal.
Using the extreme values of screening impacts and the mortality rates specific to each age group, it can be estimated that mammography screening in the 50-69 age group annually prevents between 5.6 and 31.8 breast cancer deaths per 100,000 women screened. Although it is not possible to accurately estimate the impact in each age group, the impact is somewhat greater in older post-menopausal women than in younger women with a higher breast density.
Screening enables early detection of breast cancer so that it is more often possible to use breast saving surgery, which may improve the patient's quality of life. Due to the rapid advancement of other treatments, it is difficult to assess as to whether screening as such results in lighter or more cost-effective treatments.
Disadvantages: The most important disadvantage of mammography screenings is that they may raise suspicions of breast cancer that turn out to be false in further examinations (false positive screening results). They give rise to concern and further diagnostic tests. After further examinations, about six in a thousand women screened are referred to surgery. The tumour is benign in a quarter of the women operated on.
An extension of screening to the 60-69 age group would increase radiation exposure, and radiation exposure, in turn, is estimated to cause 1-2 breast cancer deaths per a million women screened. False negative screening results may give a false sense of security and delay the detection of breast cancer. Some breast cancers develop slowly, and an earlier diagnosis would not necessarily produce health benefits.
Screening organisation: The supply of screening services currently varies between municipalities, thus causing inequality, which is further aggravated by the fact that screening programme participants need to pay for the services in some municipalities. According to the principles applied in screening, participation should be free of charge. All women should have access to screening services of the same standard irrespective of where they live. Any extension of screening would require more personnel and imaging equipment, which may be difficult to implement rapidly.
The service chain of breast cancer screening involves a wide range of units and professionals. Breaks in the flow of information are likely to occur, especially when local providers of screening or treatment change. The quality management of the service chains needs to be improved. If the screening programme is extended, problems may further increase.
Information provision: The information given to the women who are invited for screening is inadequate in some respects, its amount varying from one screening unit to another. Positive screening results in particular should be communicated in a manner that avoids causing any extra distress. An increased supply of information on the effects of screening to the women to be screened may affect their rate of participating in the screening programme and thus also the effectiveness of screening.
Future methods: Digital mammography is gaining a foothold as a screening method, but as yet there is no precise knowledge of its reliability compared with film mammography. Digital images can be easily interpreted outside the place of imaging, even in another country. While equipment investments may increase screening costs, the cost of mammogram assessment may be reduced through competitive tendering.
The treatment of breast cancer changes rapidly. New treatments are likely to be more effective and more expensive than old ones. If the impacts of screening and treatment are looked at in combination while assessing the cost-effectiveness of a screening programme, a single new effective medicine for cancer may considerably affect the assessment result.