How risks of breast cancer and benefits of screening are communicated to women: analysis of 58 pamphlets

British Medical Journal, July 25, 1998 by Emma K. Slaytor, Jeannette E. Ward

Informed participation in population based screening programmes requires an explicit sharing of information about risks and benefits? However, many factors influence perceptions of risk and the value of risk reduction promised through screening. Campaigns that selectively quote incidence to "frighten" women into undergoing mammography have been criticised.[2] Perceived risk, not objective risk, explains readiness to undergo screening in most models of health behaviour. Furthermore, the willingness of health purchasers to fund mammographic screening has been shown to be significantly influenced by the way in which data about effectiveness are presented: a programme achieving a 30% reduction in relative risk was more likely to be funded than two others described in terms of absolute risk reduction or numbers needed to screen to avert one death from breast cancer, even though all three were objectively identical in effectiveness? No studies have examined how risks of breast cancer and benefits of screening are communicated to women themselves.

Methods and results

In July 1997 we telephoned all cancer organisations, health departments, and mammographic screening programmes throughout Australia and asked for any information leaflets currently available for women about mammography. For each brochure, EKS used a 10 item score sheet to record its content. Independent assessment was performed by another staff member. Discrepancies were noted and resolved by consensus.

All organisations responded, resulting in 58 brochures. Independent agreement between the assessors was 98.9%. Lifetime risk of developing breast cancer was the most commonly stated risk (table), with considerable variation of estimates ranging from one in 11 to one in 16. Only one brochure provided information about the risk of dying from breast cancer. Three provided information about survival from breast cancer but only as "more than 70% of women survive" "two thirds of women survive" and "most women outlive this disease"

Information about risks and benefits of mammographic screening in 58 Australian pamphlets for women

Information provided                           No (%) of pamphlets
Lifetime risk of developing breast cancer          35 (60)
Lifetime risk of dying from breast cancer           1 (2)
Survival from breast cancer                         3 (5)
Relative risk reduction                            13 (22)
Absolute risk reduction                              0
Numbers needed to screen to avoid one
  death from breast cancer                           0
Proportion of screened women who
  would be recalled                                  8 (14)
Proportion of-breast cancers detected
  by mammography (sensitivity)                      15 (26)
Proportion of women without breast cancer
  who would have a positive                          0
  mammogram (specificity)
Proportion of women with a positive
  mammogram who would have breast                    0
  cancer (positive predictive value)

Relative risk reduction was the epidemiological information most often provided to communicate the benefits of mammographic screening (table), but the estimates included "about 30%," "about 40%" and "up to 50%" and six pamphlets from one state advised unequivocally that "women who have regular screening mammograms every two years halve their chances of dying from breast cancer." No pamphlets expressed benefit as absolute risk reduction or numbers needed to screen.

Information about the accuracy of screening tests was provided only occasionally. Sensitivity was expressed as: "mammograms pick up 90% of breast cancers." Six brochures stated that mammograms "are not 100% accurate (or foolproof)" without giving any detail.

Comment

Our study is the first to show the emphasis on incidence rather than mortality to communicate the risk of breast cancer to women. Since mammographic screening reduces mortality but not incidence,[2] this partiality is worrying. In addition, mammographic screening increases the incidence of breast cancer by detecting innocuous disease that would never become clinically important. Thus, it is a circular argument to encourage participation in mammographic screening only because of an increasing number of cases.

The benefits of mammography were reported inconsistently and only ever as relative risk reduction and never as absolute risk reduction or numbers needed to screen to change an outcome for one woman. In a compelling reflection on mammographic screening in the United Kingdom, Maureen Roberts argued for a "truthful account of the facts" to be given to women: "It will not be what they want to hear."[4] Ominously, perhaps, the provision of specific risk information discourages participation in mammography? If, like purchasers' willingness to pay,[3] women's participation in screening can be manipulated by partial disclosure of epidemiological data, then informed decision making by consumers necessitates a disinterested presentation of all pertinent facts.