Breast cancer is the most common cancer among women worldwide, and there are several possible methods for screening.
If facilities are available, screening by mammography alone, with or without physical examination of the breasts, plus follow-up of individuals with positive or suspicious findings, will reduce mortality from breast cancer by up to one-third among women aged 50–69 years (IARC, In press).
Much of the benefit is obtained by screening once every 2–3 years. There is limited evidence for its effectiveness for women 40–49 years of age (IARC, In press)(see Figure 5.2). The Health Insurance Plan (HIP) study, which used physical examinations by surgeons, suggested benefits in younger women only after they had reached their fifties (Shapiro, 1997). A cohort study in Finland suggested breast self-examination to be of benefit at all ages (Gastrin et al., 1994), as did a case-control study in Canada (Harvey et al., 1997).
However, observational studies of these latter types cannot exclude selection bias and may overestimate benefit. A randomized trial of breast self-examination in China has not found any evidence of reduction in breast cancer mortality after long-term follow-up (IARC, In press). This suggests that a programme to encourage breast self-examination alone would not reduce mortality from breast cancer. Women should, however, be encouraged to seek medical advice immediately if they detect any change in a breast that suggests breast cancer.
Unfortunately, mammography is an expensive test that requires great care and expertise both to perform and in the interpretation of results. It is therefore currently not a viable option for many countries. Although there is inadequate evidence that physical examination of the breasts as a single screening modality reduces mortality from breast cancer (IARC, In press), there are indications that good clinical breast examinations by specially trained health workers could have an important role. These come from the HIP study where mammography detected a low proportion of breast cancers, especially in women under the age of 50 (Shapiro, 1997), yet breast cancer mortality was reduced. Similarly, in the Canadian National Breast Screening Study, where the addition of mammography to such examinations in women aged 50–59 did not result in a reduction in breast cancer mortality (Miller et al., 2000a).
Given the present level of evidence, the national cancer control programme should not recommend screening by breast self-examination and physical examinations of the breast. Rather, the programme should encourage early diagnosis of breast cancer, especially for women aged 40-69 years who are attending primary health care centres or hospitals for other reasons, by offering clinical breast examinations to those concerned about their breasts and promoting awareness in the community. If mammography is available, the top priority is to use it for diagnosis, especially for women who have detected an abnormality by self-examination. It should be borne in mind, however, that cancer may be present even if the mammogram is negative. Mammography should not be introduced for screening unless the resources are available to ensure effective and reliable screening of at least 70% of the target age group, that is, women over the age of 50 years.
In determining the relative priorities for different screening programmes, it is important to recognize that breast cancer screening is intrinsically less effective than cytological screening for cervical cancer. As a rough guide, screening will produce an equivalent reduction in numbers of deaths in the two conditions only if, in the absence of screening, breast cancer mortality is three times that of cervical cancer in the age groups concerned.