Informed consent for mammography screening: modelling the risks and benefits for American women.

INTRODUCTION: In order to facilitate informed decision making, women require information on the probabilities of different outcomes with mammography screening. This paper derives these probabilities for a US population and illustrates them visually in a readily understandable format.
METHODS: Probabilities of the breast cancer mortality, all cause mortality and further investigation are derived from published data on mortality from breast cancer and published estimates of effectiveness using a life-table method. Probabilities are calculated of surviving to age 75 from age 40 with and without two-yearly mammography screening from age 40 and age 50. Probabilities are also calculated that a woman will be referred for further assessment or biopsy or die from breast cancer despite screening. To avoid being misled, these outcomes are presented in the form of a single decision aid illustrating the outcomes for 1000 women choosing each alternative: mammography screening or no mammography screening.
RESULTS: Of 1000 women undergoing two-yearly mammography screening from age 40 an additional four (3.7 per 1000) will reach the age of 75; of the survivors 514 will be referred for further investigation and 138 will undergo biopsy. Of 1000 women screened from age 50 an additional three (3.3 per 1000) will reach age 75; of the survivors 408 will be referred for further investigation and 94 will undergo biopsy. Mammography from age 40 to 49 reduces mortality by 0.4 in 1000. This information is readily presented visually.
CONCLUSIONS: It is possible to provide realistic estimates of the effects of mammography screening on mortality in a readily understandable format. Women require this information if they are to make informed choices about mammography screening.