The prevalence of metastatic breast cancer in Australia

As in most countries, including those with well-developed registries, Australia faces a critical gap in the cancer data collection needed for direct measurement of prevalence of metastatic cancer (including metastatic breast cancer (MBC)).

In the absence of nationally available contemporary data, and to shine a light on this issue, BCNA estimated at least 10,600 Australians living with MBC in 2020 (BCNA 2022), based on findings from earlier research in NSW (Clements et al 2012) applied to Australia’s breast cancer population in 2020. However, in 2024 CINSW estimated MBC prevalence in NSW using new methods which suggested that this national estimate was likely to be significantly underestimated (NSW Health, 2024).

This project aims to produce a more reliable estimate of the prevalence of MBC in Australia using currently available data.

Estimated prevalence of metastatic breast cancer in 2024

The AIHW has estimated that there were around 20,800 women and 150 men living with MBC in 2024 (Table 1).

These first national numbers are estimates based on the best currently available national data. The estimates involve a number of assumptions and recognise limitations in the data.

The number of women living with MBC reported by AIHW may differ from estimates reported by states and territories.

AIHW estimates for NSW, Victoria and Queensland differ from the counts previously produced by CINSW, CCV and CAQ, reflecting differences in the available data and completeness of counts, the assumptions used to model national estimates, and advice received during consultation with experts from each of these states. Future work in this project will examine these differences using the National Health Data Hub to further refine the national estimates. 

Table 1 describes the number of women estimated to be living with MBC in 2024, in Australia and in Australian states and territories.

Table 1: Estimated number of Australian women living with metastatic breast cancer at the end of 2024, by state of residence at the time of MBC diagnosis

State/territory

Number of women

NSW

5,900e

Vic

5,400e

Qld

4,600e

WA

2,000

SA

1,800

Tas

510

ACT

370f

NT

170f

Australia

20,800

Notes:

  1. Estimates have been rounded to the nearest 10 (for small numbers) or 100 (for large numbers).
  2. Rows will not add to total due to rounding errors, and because for 50 out of the 20,800 cases, there was insufficient information to identify state of residence.
  3. In addition to these women, approximately 150 Australian men are also estimated to have been living with MBC at the end of 2024.
  4. The MBC prevalence numbers presented in the table above for all jurisdictions are modelled estimates and are based on a number of assumptions. Estimates should be considered preliminary and indicative.
  5. CINSW, CCV and CAQ have each derived their own counts for NSW (NSW Health 2024), Victoria (BCNA 2025a) and Queensland (BCNA 2025b) and based on state-specific data that is more detailed than the data available to AIHW.
  6. Estimates for the NT, and to some extent the ACT, should be used especially cautiously due to what appear to be greater opportunity for linkage errors for these jurisdictions in CaT-Link. These issues are discussed in more detail in the methods paper.

Source: AIHW analysis of CaT-Link data, and adjustment with reference to CINSW, CCV and CAQ estimates.

These estimates are for a specific point in time –2024 – and this work cannot accurately measure changes in MBC prevalence from previous years. However, two major determinants of prevalence are the number of new cases (incidence) and survival. From existing data, it appears probable that both incidence and survival are increasing, meaning that the number of people living with metastatic breast cancer is likely to grow over time.

While 5-year relative survival for stage IV breast cancer (where a person was at stage IV at the time of diagnosis) was 32% in 2011 (AIHW 2019), several hundred (potentially a thousand) people diagnosed with MBC between 2002 and 2010 were estimated to be still alive in 2024 (even after accounting for the possibility of linkage error).

Methods used to estimate prevalence, along with assumptions and limitations, are outlined in the technical section. More detailed descriptions of the methods used are provided in the methods paper.

Box 1: Progressively better estimates and national data development

Improved data is necessary to inform the development of more effective treatment and the capacity of all governments to support people diagnosed with cancers generally and metastatic breast cancer specifically.

National linked cancer and treatment data capacity is anticipated to improve substantially with the scheduled addition of cancer incidence data to the AIHW’s National Health Data Hub, with the first few states agreeing to link their cancer registry data into the Hub. This will allow AIHW to bring together information on incidence, treatment (including hospitals, MBS and PBS) and outcomes (including aged care data and deaths) over the coming year.

More robust estimates or actual counts of MBC are anticipated to become increasingly possible as this capacity expands, as does the possibility of reporting on survival and a range of other issues.

Collaborative work through the Australian Cancer Data Alliance, with state and territory cancer registries and health departments, and AIHW, also seeks to improve the amount and quality of data, and particularly of data in relation to cancer stage at diagnosis and cancer recurrence (including at metastatic stage).

 

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