Abstract
To examine breast cancer (BC) incidence trends in relation to mammographic screening and risk factor prevalence in South Australia (SA). Trends in annual BC incidence rates were calculated using direct standardisation and compared with projected incidence derived from Poisson regression analysis of pre-screening rates. Annual percentage change and change time points were estimated using Joinpoint software. Biennial mammography screening participation rates were calculated using data from BreastScreen SA. Trends in overweight/obesity, alcohol use and hormone replacement therapy (HRT) use were examined using 1991-2009 Health Omnibus Survey data. Trends in total fertility were examined using data from the Australian Bureau of Statistics. BC incidence increased around the time BreastScreen commenced and then stabilised in the mid-1990s. However rates have remained higher than projected, even though the proportion and age distribution of first time screening attendees stabilised around 1998. A decrease in BC incidence was observed among women aged 50-59yrs from the late-1990's but not among older women. Obesity and alcohol use have increased steadily in all age groups, while HRT use declined sharply from the late-1990s. BC incidence has remained higher than projected since mammography screening began. The sustained elevation is likely to be due to lead time effects, though over-diagnosis cannot be excluded. Declining HRT use has also impacted incidence trends. Studies using individual level data, which can account for changes in risk factor prevalence and lead time effects, are required to evaluate 'over-diagnosis' due to screening.
Highlights
Breast cancer is the leading cancer among women world-wide (International Agency for Research on Cancer, 2008)
We describe changing patterns of participation in mammography screening, as well as changes in the prevalence of hormone replacement therapy (HRT) use and other %&ULVNIDFWRUVLQWKHSRSXODWLRQ2XUVWXG\VSHFLÀFDOO\ addresses the following questions: Have breast cancer (BC) incidence rates increased beyond projected rates based on prescreening incidence trends?; At what time points did BC incidence trends increase, stabilise or decrease?; Do any of these changes coincide with the commencement of the organised screening and or stabilisation of screening SDUWLFLSDWLRQDQGZHUHWKHUHDQ\VLJQLÀFDQWFKDQJHVLQ ULVN IDFWRU SUHYDOHQFH WKDW PLJKW DOVR KDYH LQÁXHQFHG incidence trends?
Our results indicate that BC incidence increased substantially around the time organised mammography screening was introduced in South Australia (SA), suggesting a strong of HRT use decreased after a period of high use during the early 1990s
Summary
Breast cancer is the leading cancer among women world-wide (International Agency for Research on Cancer, 2008). Changes in reproductive SUDFWLFHV HJIHZHUFKLOGUHQROGHUDJHDWÀUVWELUWK DQG lifestyle factors (e.g. increasing body weight, decreasing physical activity, alcohol use, hormone use) and improved health and nutrition (leading to taller statue, younger age at menarche, older age at menopause) may have contributed to the increasing incidence globally (Bray et al, 2004). Possible explanations include the maturation of screening programs (Jemal et al, 2007; Gompel and Plu-Bureau, LH RQFH WKH SURSRUWLRQ DQG DJH RI ÀUVWWLPH screeners stabilises incidence effects of screening should stabilise), declining participation in mammography screening (Gompel and Plu-Bureau, 2010), and, or the sudden decline in hormone therapy use (Glass et al, 2007; Zbuk and Anand, 2012) following results of the Women Health Initiative (WHI) trial (Chlebowski et al, 2003)
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