In Reply We appreciate the thoughtful comments from Molini茅 et al regarding our recent publication on the global stage distribution of breast cancer at diagnosis.¹ Their insights particularly about the staging of breast cancer in France provide an opportunity for further clarification and discussion.

Our study¹ aimed to provide a comprehensive overview of the distribution of breast cancer stage at diagnosis worldwide. Yet we acknowledged important variations in stage recording and reporting across countries that are linked to the availability and use of multiple staging systems and their evolution, as well as recording practice, standards used, and completeness of data from sources that are available to population-based registries (PBCRs).^2,3 The point raised regarding the classification of 鈥渁dvanced stage鈥� breast cancer in France, which was based on the European Network of Cancer Registries (ENCR) guidelines on the condensed TNM for Coding Extent of Disease,⁴ encompassing both nonresected cancers without visceral metastasis and metastatic cancers, is an important aspect of such variation in standards used and practices in registries.¹ The condensed TNM system was developed as a simplified staging system to allow PBCRs to overcome complexities in collecting stage information, yet, has not been considered widely by European registries who rather opt for the TNM system.⁵ The aim of our study was to understand the variation of proportions of metastatic breast cancer across countries, as such we prioritized studies that reported using TNM classification (stage IV or M1) or SEER (distant). In this article, we acknowledged that data from 2 countries (France and Poland) were only available based on a condensed TNM system that would group both metastatic and nonresectable tumors in the advanced stage category. It is imperative to note that our meta-analysis integrated data from various sources, each with their methodologies and categorizations. Although we endeavored to maintain consistency and accuracy, the heterogeneity of data is an inherent challenge in such large-scale analyses.¹ Although highlighted in our original publication, we would like to emphasize that the condensed TNM classification mentioned by Molini茅 et al could indeed inflate the perceived distribution of metastatic breast cancer in France compared with other countries. However, it is crucial to emphasize that our analysis, despite these limitations, provides valuable insights into the global patterns of breast cancer diagnosis. These findings have significant implications for public health policies, resource allocation, and awareness campaigns.¹

The French Network of Cancer Registries (FRANCIM) is an important network that provides essential information on the diagnosis and burden of cancer across France. We thank Florence Morine and colleagues⁶ for bringing to our attention their more recently published report that shows 7.3% of metastatic breast cancer diagnoses in France from 2009 to 2015, which is more consistent with what we observed in other European countries of comparable health care systems. We would like to reiterate the findings of this report, particularly to French stakeholders and policymakers, and to ensure that the distribution of metastatic breast cancer in France and older patients aligns with other European countries.

We agree with the authors that accurate stage categorization is fundamental for interpreting cancer epidemiology data correctly. This discussion underlines the need for standardized cancer staging reporting globally to facilitate more accurate and comparable research. Current international initiatives including the Global Initiative for Cancer Registry Development (GICR) and essential TNM² from IARC are integral in supporting cancer registries globally to support a standardized collection and registration of high-quality, comparable data on cancer incidence, including stage at diagnosis. Although acknowledging the limitations and variability in staging data, our study contributes to understanding the global burden of breast cancer. We hope that it will inspire further research and discussions, leading to improved cancer care and outcomes worldwide.

Corresponding Author: Isabelle Soerjomataram, MD, PhD, Cancer Surveillance Branch, International Agency for Research on Cancer, 25 Ave Tony Garnier, Lyon, France (soerjomatarami@iarc.who.int).

Published Online: April 25, 2024. doi:10.1001/jamaoncol.2024.0671

Conflict of Interest Disclosures: None reported.