Population screening and intensity of screening are associated with reduced breast cancer mortality: evidence of efficacy of mammography screening in Australia
- 1.1k Downloads
Efficacy of breast screening may differ in practice from the results of randomized trials. We report one of the largest case–control evaluations of a screening service.
Subjects included 491 breast-cancer deaths affecting 45–80-year-old South Australian females during 2002–2005 (diagnosed after BreastScreen commencement) and 1,473 live controls (three per death) randomly selected from the State Electoral Roll after birth-date matching. Cancer Registry and BreastScreen records provided cancer and screening details. Risk estimates were calculated by BreastScreen participation, using conditional logistic regression. Interpretation was assisted by a population survey of risk factor prevalence by BreastScreen participation in 1,684 females aged ≥40 years.
The relative odds (OR) (95% confidence limits) of breast-cancer death in BreastScreen participants compared with non-participants were 0.59 (0.47, 0.74). Compared with non-participants, the OR was 0.70 (0.47, 1.05) for women last screened through BreastScreen more than 3 years before diagnosis of the index case, and 0.57 (0.44, 0.72) for women screened more recently. The OR of 0.47 (0.34, 0.65) for women screened more frequently in the pre-diagnosis phase was lower than the 0.64 (0.50, 0.82) for other screened women. The overall OR of 0.59 approximated 0.70 when corrected for the screening self-selection bias observed in five randomized trials. However, multivariable analysis of survey data did not indicate a lower prevalence of breast-cancer risk factors among BreastScreen participants, suggesting that this correction may be inappropriate.
Participation in screening was associated with a breast-cancer mortality reduction of between 30 and 41%, depending on assumptions about screening self-selection bias. A downward mortality risk by recency of last screen prior to cancer diagnosis, and frequency of recent screening, is consistent with a screening effect.
KeywordsPopulation screening Breast neoplasm Breast cancer mortality Mammography Self-selection bias
The authors are indebted to Jill Rogers of BreastScreen South Australia and Jennifer Owen of The Cancer Council South Australia for extracting the data required for this study from source records.
- 4.Tabar L, Fagerberg G, Duffy S, Day N, Gas A, Grontoft O (1998) Update of the Swedish two county program of mammographic screening trial. Radiol Clin North Am 51:81–91Google Scholar
- 6.Miller AB, Baines CJ, To T, Wall C (1992) Canadian national breast screening study, 1: breast cancer detection and death rates among women aged 40 to 49 years. Can Med Assoc J 147:1459–1476Google Scholar
- 7.Miller AB, Baines CJ, To T, Wall C (1992) Canadian national breast screening study, 2: breast cancer detection and death rates among women aged 50 to 59 years. Can Med Assoc J 147:1477–1488Google Scholar
- 10.World Health Organization (WHO), International Agency for Research on Cancer (IARC) (2002) IARC handbooks of cancer prevention, vol 7: breast cancer screening. IARC Press, LyonGoogle Scholar
- 13.South Australian Cancer Registry (1996) Epidemiology of cancer in South Australia. Incidence, mortality and survival, 1977 to 1995. Incidence and mortality, 1995. Openbook Publishers, AdelaideGoogle Scholar
- 14.Roder D (2006) Population screening—opportunities to strengthen cancer control. Public Health Bull S Aust 5:2–6Google Scholar
- 16.Armitage P, Berry G (1987) Statistical methods in medical research, 2nd edn. Blackwell Scientific Publications, OxfordGoogle Scholar
- 17.StataCorp (2005) Stata statistical software. Release 9.2. StatCorp LP, College Station, TXGoogle Scholar
- 19.Australian Bureau of Statistics (1998) 1996 census of population and housing. Socio-economic indexes for areas. Australian Bureau of Statistics, CanberraGoogle Scholar
- 20.Department of Health and Aged Care and the University of Adelaide (1999) Measuring remoteness: accessibility/remoteness index of Australia (ARIA). Occasional Papers: New Series No. 6. Commonwealth of Australia, CanberraGoogle Scholar
- 21.Government of South Australia, Department of Health, Population Research and Outcomes Studies Unit (2006) Health Monitor, July and September, 2006. BreastScreen data report. Department of Health, AdelaideGoogle Scholar
- 22.Duffy SW, Hill C, Esteve J (eds) (2001) Quantitative methods for the evaluation of cancer screening. Oxford University Press, New YorkGoogle Scholar
- 31.Feig SA (1996) Methods to identify benefit from mammographic screening in women aged 40–49 years. Editorial. Radiology 201:309–316Google Scholar
- 32.Duffy SW, Cuzick J, Tabar L et al (2002) Correcting for non-compliance bias in case-control studies to evaluate cancer screening programmes. Appl Stat 51:235–243Google Scholar