Trends in stage-specific breast cancer incidence and overdiagnosis in NSW Presented by Dr Gemma Jacklyn Sydney School of Public Health @gemmajacklyn Authors Gemma Jacklyn, Kevin McGeechan, Les Irwig, Nehmat Houssami, Stephen Morrell, Katy Bell, Alexandra Barratt
Background Two prerequisites for screening to lower cancer mortality 1. Screening must bring forward in time the diagnosis of cancers destined to cause death Find more early-stage cancer BUT Must be followed by a decline in late-stage cancer 2. Early treatment of cancers destined to cause death must provide some benefit over late treatment after clinical presentation Stage-specific incidence of breast cancer in NSW
Effective screening Fig 1. Optimal screening program 200 180 Incidence 160 140 120 100 Early-stage cancer Overall cancer rate 80 60 Late-stage cancer 40 20 0 Introduction of screening 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 Time Stage-specific incidence of breast cancer in NSW
Aims Examine temporal trends in the incidence of early- and late-stage incidence of breast cancer in NSW women Estimate the percentage risk of overdiagnosis attributable to screening mammography in NSW Stage-specific incidence of breast cancer in NSW
Methods Setting: NSW, Australia from 1972-2012 Participants: Stage: Women of all ages with a histologically verified breast cancer diagnosis recorded in the NSW Cancer registry Overdiagnosis: Women aged 50 years and older Intervention: BreastScreen NSW (1988-2012) Measurement: Early-stage cancer (carcinoma in situ & localised) Late-stage cancer (regional & distant metastases) Stage-specific incidence of breast cancer in NSW
Methods: stage Analysed trends over 25 years to allow surplus of early-stage cancer to translate into decrease in late-stage cancer Rates were standardised by 5-year age intervals within broad age groups, using the Australian 2001 population. Stage-specific incidence of breast cancer in NSW
Heading Results: stage Pre-screening Medicare BreastScreen mammography roll-out Pilot screening Established screening Digital Early-stage Breast cancer incidence (cases/100,000 women) Late-stage Women aged 50 years and older Early-stage Late-stage Women younger than 50 years Figure 2. Incidence of Stage-Specific Breast Cancer in NSW women, 1972 2012 Note: Rates were standardised by 5-year age intervals within broad age groups, using the Australian 2001 population.
Heading Results: stage Figure 3. Incidence of Stage-Specific Breast Cancer in NSW women aged 50-69 years, 1972 2012 Note: Rates were standardised by 5-year age intervals within broad age groups, using the Australian 2001 population.
Results: stage Incidence for all stages higher than prescreening levels The number of women diagnosed with early-stage breast cancer at diagnosis has tripled No decrease in incidence of late-stage breast cancer at diagnosis In women too young to screen the incidence of late-stage breast cancer also increased, whereas localised disease was stable Stage-specific incidence of breast cancer in NSW
Methods: overdiagnosis Estimate of expected incidence in unscreened women 1. Poisson regression modelling to estimate annual counts of early- and late-stage breast cancer in NSW women from 1988-2012; 2. Incidence trends in contemporary cohort of NSW women who did not attend screening regularly (age 40-44 years). Adjustment for changes in risk factors Capped the observed estimates of breast cancer for hormone-replacement therapy (HRT) use from 1988-2004 Overdiagnosis of breast cancer in NSW
Methods: overdiagnosis Calculation: Calculated difference in observed counts relative to the expected in each subsequent calendar year Excess cancers / cancers diagnosed in women invited to screening Lead time adjustment: 1. Included cancer cases in women who were older than the upper age limit of the screening program. 2. Analysed trends over 25 years to allow for equilibrium between initial incidence peak and compensatory drop Overdiagnosis of breast cancer in NSW, Australia
Heading Results Table 1 Overdiagnosis in NSW women aged 50 years and older invited to screening, 2010-2012 Method DCIS Invasive Distant Total Prescreening trend (women aged 50+) Contemporary trend (women aged 40-44) 13.4% 23.0% -7.1% 29.3% 13.6% 25.5% -15.9% 23.1% Overdiagnosis of breast cancer in NSW, Australia
Results Overdiagnosis does not simply involve DCIS more than half are invasive breast cancer Around one quarter of all newly diagnosed DCIS and invasive breast cancer cases in women aged 50+ are overdiagnosed Approximately 5 additional cases of breast cancer are detected for every metastatic breast cancer prevented Overdiagnosis of breast cancer in NSW, Australia
Strengths & limitations 40 years of data on histologically verified stage-specific breast cancer at diagnosis Observational study design Don t know what the trends would have been in the absence of screening Stage-specific incidence of breast cancer in NSW
Conclusion Screening mammography was not associated with a reduction in the incidence of late-stage breast cancer in NSW We estimate that around one quarter of all breast cancer cases are overdiagnosed Some of the expected benefits of screening mammography in NSW may not have been realised Overdiagnosis of breast cancer in NSW, Australia
Publication details Jacklyn G, McGeechan K, Irwig L, Houssami N, Morrell S, Bell K, Barratt A. Trends in stage-specific breast cancer incidence in New South Wales, Australia: insights into the effects of 25 years of screening mammography. Breast Cancer Research and Treatment 2017;66(3):843-854. doi: 10.1007/s10549-017-4443-x
Acknowledgements Stage-specific incidence of breast cancer in NSW