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Background and Purpose: In Australia and internationally, people diagnosed with metastatic breast cancer (MBC) report feeling overlooked, even invisible. A key issue contributing to MBC's 'invisibility' is that Australia's population-based cancer registries are not required to collect stage at diagnosis or recurrence data; consequently, we do not know the prevalence of MBC in Australia. MBC prevalence is a necessary indicator for planning metastatic breast cancer surveillance, treatment, and supportive care. Methods: Breast Cancer Network Australia (BCNA) consulted key stakeholders (cancer data managers, cancer registry staff, cancer epidemiologists) to understand options for determining MBC prevalence. Results: In the absence of direct prevalence counts, BCNA identified only one option for estimating national MBC prevalence. This validated method was developed in 2008 and used mathematical modelling to determine prevalence estimates from rates of breast cancer incidence and survival. Using the most recent Australian breast cancer mortality data, this model indicates that in 2020 there were 10,553 Australians living with MBC. Key stakeholders indicated that this estimate is likely to be conservative given one of the key assumptions on which the model was built – how long someone will survive with MBC – is out of date. Recent advances in metastatic treatment mean MBC survival is predicted to improve by 55% between 2005 and 2025. Extrapolating a 2004 modelled estimate for females aged 18-84 years in 2004, 12,840 will be living with MBC by 2025. Conclusion: Continued increases in survival of people with MBC reinforces Cancer Australia's 2008 statement regarding the urgent need for data on metastatic prevalence (at diagnosis and recurrence). In the interim, statistical modelling can be used to estimate prevalence. However, in the long-term, cancer registries need to be supported to collect and report metastatic data. The changes required to capture stage and recurrence data will require commitment, governance, and funding across the sector.
Durston et al. (Sat,) studied this question.