IMPORTANCE

Stage at diagnosis is a key prognostic factor for cancer survival.

OBJECTIVE

To assess the global distribution of breast cancer stage by country, age group, calendar period, and socioeconomic status using population-based data.

DATA SOURCES

A systematic search of MEDLINE and Web of Science databases and registry websites and gray literature was conducted for articles or reports published between January 1, 2000, and June 20, 2022.

STUDY SELECTION

Reports on stage at diagnosis for individuals with primary breast cancer (C50) from a population-based cancer registry were included.

DATA EXTRACTION AND SYNTHESIS

Study characteristics and results of eligible studies were independently extracted by 2 pairs of reviewers (J.D.B.F., A.D.A., A.M., R.S., and F.G.). Stage-specific proportions were extracted and cancer registry data quality and risk of bias were assessed. National pooled estimates were calculated for subnational or annual data sets using a hierarchical rule of the most relevant and high-quality data to avoid duplicates.

MAIN OUTCOMES AND MEASURES

The proportion of women with breast cancer by (TNM Classification of Malignant Tumors or the Surveillance, Epidemiology, and End Results Program [SEER]) stage group.

RESULTS

Data were available for 2.4 million women with breast cancer from 81 countries. Globally, the proportion of cases with distant metastatic breast cancer at diagnosis was high in sub-Saharan Africa, ranging from 5.6% to 30.6% and low in North America ranging from 0.0% to 6.0%. The proportion of patients diagnosed with distant metastatic disease decreased over the past 2 decades from around 3.8% to 35.8% (early 2000s) to 3.2% to 11.6% (2015 onwards), yet stabilization or slight increases were also observed. Older age and lower socioeconomic status had the largest proportion of cases diagnosed with distant metastatic stage ranging from 2.0% to 15.7% among the younger to 4.1% to 33.9% among the oldest age group, and from 1.7% to 8.3% in the least disadvantaged groups to 2.8% to 11.4% in the most disadvantaged groups.

CONCLUSIONS AND RELEVANCE

Effective policy and interventions have resulted in decreased proportions of women diagnosed with metastatic breast cancer at diagnosis in high-income countries, yet inequality persists, which needs to be addressed through increased awareness of breast cancer symptoms and early detection. Improving global coverage and quality of population-based cancer registries, including the collection of standardized stage data, is key to monitoring progress.