Outcome measures of an Australian breast-screening program

One surrogate measure of the quality and effectiveness of screening

MJA 1998; 169: 179-180  

Mammographic screening for the early detection of breast cancer is a population-based measure for which randomised controlled trials have shown a 30% reduction in mortality in women aged between 50 and 69 years and who are screened.1 It is often forgotten that Australia is one of only a few countries where the State (in the form of both Federal and State governments) funds a national program of mammographic screening. From the outset of this program, there was an insistence that a quality service was essential if the predicted mortality reduction benefits were to be realised. Thus, national quality benchmarks based on international data were set. These were incorporated into accreditation standards to apply to all services in all States and Territories. This 30% mortality reduction depended on achieving a screening rate of approximately 70% of the target population, but it was recognised that even with 100% participation an inadequate, poor-quality service would not deliver the goods. The national screening program was phased in from 1992 and now covers the whole country. The accreditation standards are achievable, but screening participation has yet to reach target, and it will be several more years before mortality statistics for breast cancer can be affected by screening. Surrogate measures for the effectiveness of the service are therefore needed. One predictor of future breast cancer mortality is the small cancer detection rate, and it is gratifying that most States and Territories have already achieved the national accreditation standard.2 Another predictor of the effectiveness of the screening program is the interval cancer rate measured at State and national levels. The interval cancer rate is usually defined as the rate of diagnosis of new cases of invasive breast cancer and ductal carcinoma-in-situ in the two-year interval after a screening examination. In this issue of the Journal Rickard et al report rates and proportional incidences of interval cancers in the 12 months after screening from a New South Wales pilot mammographic screening program.3 The proportional incidence is the proportion that interval invasive breast cancers comprise of the total number of invasive breast cancers expected in the absence of screening. While the proportional incidence reported by Rickard et al is lower than that reported in studies from the United Kingdom4 and the Netherlands,5 it is higher than that found in the Swedish Two-County Study.6 As the confidence intervals found in all these studies overlap, we cannot conclude that these differences are statistically significant. However, the lack of a statistically significant difference in the proportional incidence between the study by Rickard and colleagues3 and the Swedish one6 cannot be taken to mean that they will achieve a similar mortality reduction. Larger State-based and national studies are needed to make international comparisons. The 12-month interval-cancer incidence of 4.17 per 10 000 screens in the women aged 40-49 years and 4.64 per 10 000 screens in women aged 50-69 reported by Rickard et al3 are lower than that reported by the South Australian screening program.7 However, because the confidence intervals for the New South Wales rate3 include the SA estimate, these differences are not statistically significant. To calculate rates and proportional incidences of interval cancers, we need well-functioning, complete and up-to-date BreastScreen services and cancer registries in each of the States and Territories. This requires both political will and financial resources, at national and State levels. It is also essential that each program counts interval cancers in the same way. In the UK,8 different definitions of interval cancers gave estimates of the interval cancer rate which varied by nearly 30%. While the low 12-month incidence rate found by Rickard et al is promising, it is also important to measure this in the second year after screening, when interval cancers are likely to form a greater proportion of the expected incidence of breast cancer. Also, although this study is too small to present separate interval cancer rates for the first and second screening round, future studies must do this, as these rates may differ. Nevertheless, it is essential to recognise the need to measure interval cancer rates in breast screening in a consistent fashion, in each State and Territory as well as nationally. Although interval cancers are inevitable, they are a measure of the sensitivity of a program whose object is to ensure that a high proportion of women with cancer are diagnosed by the screening process. However, achieving the lowest possible interval cancer rate must not be done at the expense (financial and emotional) of recalling a high proportion of women for further assessment that would lead to high rates of false positives (as happened in one American service where one-third of women without cancer received an abnormal screening result over 10 years).9 BreastScreen Australia is just over five years old and in its infancy. It has attained a high level of awareness among women,10 with very high levels of acceptability as shown by high rescreening levels.11 Government funding permits a quality of screening not available in the world's first national program, in the United Kingdom -- double-view mammography, double specialist reading and a two-yearly screening interval. To ensure quality and to assess whether their stewardship of this national investment in women's health is likely to have produced the expected reduction in breast cancer mortality, programs should be encouraged not only to attain the accreditation standards, but also to use nationally agreed surrogate measures for overall mortality changes, of which interval cancer rates are but one. Further, governments must support their investment by encouraging and funding the collection and interchange of these nationally agreed data. Alan Rodger Professor and Director The William Buckland Radiotherapy Centre, The Alfred Health Care Group, Melbourne, VIC Anne M Kavanagh Public Health Research Fellow Cancer Epidemiology Centre, Anti Cancer Council of Victoria, Melbourne, VIC Hurley SF, Kaldor JM. The benefits and risks of mammographic screening for breast cancer. Epidemiol Rev 1992; 14: 101-103. National Program for the Early Detection of Breast Cancer -- national accreditation requirements: March 1994. Canberra: Commonwealth Department of Human Services and Health, December 1994. Rickard MT, Taylor R, Fazli MA, El Hassan N. Interval breast cancers in an Australian mammographic screening programme. Med J Aust 1998; 169: 184-187. Woodman CBJ, Threlfall AG, Boggis CRM, Prior P. Is the three year breast screening interval too long? Occurrence of interval cancers in NHS breast screening programme's north western region. BMJ 1995; 310: 224-226. Peeters PHM, Verbeek ALM, Hendricks JHCL, et al. The occurrence of interval cancers in the Nijmegen screening programme. Br J Cancer 1989; 59: 929-932. Tabar L, Faberberg G, Day NE, Holmberg L. What is the optimum interval between mammographic screening examinations? An analysis on the latest results of the Swedish two-county breast cancer screening trial. Br J Cancer 1987; 55: 547-551. Robinson JL, Crane CEB, King JM, et al. The South Australian breast x-ray service: results from a statewide mammographic screening programme. Br J Cancer 1996; 73: 837-842. Faux AM, Richardson DC, Lawrence GM, et al. Interval breast cancers in the NHS breast screening programme: does the current definition exclude too many? J Med Screening 1997; 4: 169-173. Elmore JG, Barton MB, Moceri VM, et al. Ten-year risk of false positive screening mammograms and clinical breast examination. N Engl J Med 1998; 338: 1089-1096. Barratt AL, Cockburn J, Redman S, Perkins PC. Mammographic screening: results from the 1996 National Breast Health Survey. Med J Aust 1997; 167: 521-524. BreastScreen Victoria. Annual Statistical Report 1996. Melbourne: Victorian Breast Screening Co-ordination Unit Inc., 1996: 12.