Performance indicator 7b: Ductal carcinoma in situ (DCIS) incidence
Summary
- In 2021, 2,368 new cases of DCIS were diagnosed in women in Australia, which is an incidence rate of 18.3 new cases per 100,000 women.
- In 2021, 1,716 new cases of DCIS were diagnosed in women aged 50–74 in Australia, which is an incidence rate of 47.5 new cases per 100,000 women.
Definition
The number of new cases of ductal carcinoma in situ (DCIS) in women aged 50–74 per 100,000 estimated resident female population in a calendar year.
Rationale
DCIS incidence data provide information about the underlying level of DCIS in Australia. DCIS is known as a ‘disease of screening’ and was rarely detected before breast screening was introduced. Since the introduction of screening mammography, detection of DCIS has increased. Annual monitoring of these data by various groupings (such as age or location) may reveal findings of concern or positive trends that can be used to inform BreastScreen Australia as well as broader policies for DCIS in Australian women.
Guide to interpretation
These data include both screen-detected DCIS cases (through BreastScreen Australia) and DCIS cases detected outside the screening program.
DCIS incidence data are reported per 100,000 females in the population.
To produce reliable rates from the relatively small number of DCIS cases, incidence of DCIS is reported by 10-year age groups.
The Australian Cancer Database (ACD) is the source of DCIS incidence data.
The counting rules for DCIS incidence were revised for the 2016 ACD. For this reason, comparisons should not be made with DCIS data from previous versions of the ACD.
See Box 7.3 for more details.
The most recent incidence of DCIS data are for new cases diagnosed in 2021.
Results
In 2021, the latest year of national data available in the Australian Cancer Database, there were 2,368 new cases of DCIS diagnosed in women of all ages in Australia, which is 18.3 new cases per 100,000 women in the population (15.6 new cases per 100,000 women after adjusting for age to allow comparison over time or across population groups).
Of these, 2,368 new cases, 1,716 (72.5%) occurred in women aged 50–74 (the target age group for BreastScreen Australia), which is equivalent to 47.5 new cases of DCIS per 100,000 women aged 50–74 (46.3 new cases per 100,000 women aged 50–74 after adjusting for age to allow comparison over time or across population groups).
Box 7.3: Changes in counting rules for DCIS incidence in the 2016 ACD
The counting rules for DCIS incidence were revised for the 2016 ACD. This affects the counts for women who have been diagnosed with both an invasive and an in situ ductal carcinoma. In previous versions of the ACD, a woman’s first DCIS was always counted. Starting with the 2016 ACD, a woman’s first DCIS is counted if it is diagnosed before their first invasive ductal carcinoma but not counted if it is diagnosed at the same time or afterwards. This change brings the counting rules for DCIS into line with the rules for counting multiple invasive ductal carcinomas. The new rules lead to lower counts and rates of DCIS incidence than the old rules. For this reason, comparisons should not be made with DCIS data from previous versions of the ACD.
Box 7.4: DCIS cases detected through BreastScreen Australia
Around 4 in 5 (79.4%) DCIS cases diagnosed in 2021 in women aged 50–74 were detected through BreastScreen Australia (68.1%) for DCIS cases diagnosed in 2021 in women aged 40 and over.
DCIS incidence by age
Similar to invasive breast cancer, the incidence of DCIS increases with increasing age.
In 2021, the age specific incidence rate of DCIS per 100,000 women rose from 20.4 new cases for women aged 40–49 to 49.8 for those aged 60–69 before falling to 37.6 for those aged 70 and over.
In 2021, DCIS in women aged 50–74 represented 72.5% of all DCIS cases diagnosed in that year.
DCIS incidence trends
DCIS incidence rates have increased over time. For women aged 50–74, the age-standardised DCIS rate per 100,000 women rose from 40.6 new cases in 2002 to a peak of 55.1 in 2014, before falling to 46.3 new cases in 2021.