Summary

This is the second report from an Australian-first project, combining data from BreastScreen Australia, the National Cervical Screening Program, the National Bowel Cancer Screening Program, the Australian Cancer Database, the National Death Index, and the National HPV (human papillomavirus) Vaccination Program Register.

While the first report (AIHW 2018a) presented primary cancer outcomes for the target age groups for all three cancer screening programs, as well as examining screening behaviour across the three cancer screening programs, this report focuses on breast cancer outcomes and screening behaviour that are relevant to BreastScreen Australia.

Building on breast cancer outcomes for women in the BreastScreen Australia target age group of 50–69, these results also include age groups eligible to attend, but outside the target age group (note that the current target age group of 50–74 was not applicable to this project). Additionally, these results include outcomes using different correction factors for lead-time bias and screening selection bias that may be more appropriate for these Australian data. Screening behaviour analyses focus on key areas identified to be of particular interest and value to BreastScreen Australia.

The following analyses compare survival outcomes of breast cancers detected through BreastScreen Australia with breast cancers diagnosed in women who had never screened through BreastScreen Australia. For the years of data included, women aged 50–69 were targeted for screening, but were eligible to screen when aged 40–49 or 70 or over.

Breast cancers diagnosed in women targeted by BreastScreen Australia

Of the 73,440 breast cancers diagnosed in women aged 50–69 in 2002–2012:

  • 31,968 (44%) were detected through BreastScreen Australia
  • 20,245 (28%) were diagnosed in women who had never screened.

Breast cancers detected through BreastScreen Australia had a 69% lower risk of causing death before 31 December 2015 (the end of follow-up) than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

After correcting for lead-time bias (where an earlier diagnosis may not affect date of death, yet give a seemingly longer survival time) and screening selection bias (where women who participate in screening may have a different risk of death than those who do not) using lead times and correction factors deemed most appropriate for Australian women aged 50–69, breast cancers detected through BreastScreen Australia had a 54% to 63% lower risk of causing death than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

This indicates that it is beneficial for a breast cancer to be detected through screening mammography rather than due to the breast cancer being symptomatic. This may be due to breast cancers detected through BreastScreen Australia being at an earlier stage than breast cancers that have become symptomatic.

Although it was not possible to know the stage of the breast cancers diagnosed in this study, tumour size (one of the three factors that determine stage, along with lymph node involvement and presence of distant metastases) was recorded for most breast cancers.

In this study, 55.3% of breast cancers detected through BreastScreen Australia were found to be small, compared with 27.6% of breast cancers diagnosed in women who had never screened through BreastScreen Australia.

Breast cancers diagnosed in women eligible to attend, but not targeted by BreastScreen Australia

Of the 26,463 breast cancers diagnosed in women aged 40–49 in 2002–2012:

  • 3,461 (13%) were detected through BreastScreen Australia
  • 18,059 (68%) were diagnosed in women who had never screened.

Breast cancers detected through BreastScreen Australia had a 55% lower risk of causing death before 31 December 2015 (the end of follow-up) than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

After correcting for lead-time and screening selection bias using lead times and correction factors deemed most appropriate for Australian women aged 40–49, breast cancers detected through BreastScreen Australia had a 34% to 51% lower risk of causing death than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

Of the 37,568 breast cancers diagnosed in women aged 70 and over in 2002–2012:

  • 6,893 (18%) were detected through BreastScreen Australia
  • 20,627 (55%) were diagnosed in women who had never screened.

Breast cancers detected through BreastScreen Australia had a 64% lower risk of causing death before 31 December 2015 (the end of follow-up) than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

After correcting for lead-time and screening selection bias using lead times and correction factors deemed most appropriate for Australian women aged 70 and over, breast cancers detected through BreastScreen Australia had a 55% to 62% lower risk of causing death than breast cancers diagnosed in women who had never screened through BreastScreen Australia.

Association between cervical screening participation and participation in BreastScreen Australia

Women who were regular participants in cervical screening were more likely to participate in, and become regular screeners in, BreastScreen Australia. This effect was strongest at the age of 50—the age at which women are first invited to screen through BreastScreen Australia.

Women already participating in cervical screening began participating in BreastScreen Australia earlier than those who were not. Cervical screening participants had a mean commencement age in BreastScreen Australia of about 50, while non-participants had a mean commencement age in BreastScreen Australia that was 5 to 10 years later than this.

Rescreening behaviour in BreastScreen Australia

Rescreening within 27 months (considered to be within the recommended screening interval of BreastScreen Australia of 2 years) was about 60% after a woman’s first screening round.

This was higher after their second screening round, at about 70%, and higher again after their third or subsequent screening round, at about 80%.

Factors associated with a woman not rescreening varied by screening round. Women who did not rescreen after their first screen were more likely to report symptoms, whereas women who did not rescreen after a third or subsequent screen were more likely to have been recalled to assessment for further investigation.