Harm resulting from screening is likely to be high where prevalence of breast cancer is low

Editor—Matti Hakama and colleagues evaluated an organised programme of screening for breast cancer in Finland.1 They report a 24% reduction in mortality from breast cancer due to screening, which, as they point out, is close to the protective effect reported in the early randomised controlled trials. In their conclusions they imply that having a breast cancer screening programme is worth while and a good use of health service resources.

Such a conclusion must, however, be treated with caution. In this study the authors calculate that about 200 000 women were screened to prevent 20 deaths from breast cancer. They also quote other benefits of screening but make no mention of the well documented disadvantages.2 The most serious potential harm is that attributable to a false positive result, which can occur in about 14% of those screened.3 Thus the 20 deaths prevented must be balanced against the anxiety, trauma, and potential operative complications encountered by an estimated 28 000 women with a false positive result. To this can be added the cost to the health service of the investigations that these women will have had.

Hong Kong does not yet have an organised mammography screening programme. Since the prevalence of breast cancer is relatively low compared with that in other countries,4 the harm resulting from screening is likely to be high. This factor must also be considered when a public health decision is made on whether to introduce a screening programme.