biostudies-literatureUnknown4(1)Sopik V<h4>Background</h4>There is large variation in case-fatality rates of breast cancer in young women across the world. The objective of this study was to estimate the ten-year overall survival of women diagnosed with breast cancer before age 40 in six countries, by clinical presentation and by treatments received.<h4>Methods</h4>Data were supplied by seven centers in six countries, including the USA, Canada, Poland, Iceland, Iran and Thailand, totaling 36,861 women diagnosed with breast cancer before age 40, from 1977 to 2020. American patients from the SEER registry were sub-divided into (Non-Hispanic) White and Black. The following factors were compared across countries: year of diagnosis, tumor size, lymph node status, estrogen receptor (ER) status, use of chemotherapy, use of tamoxifen aBJC reports6https://www.ebi.ac.uk/biostudies/studies/S-EPMC12923670biostudies-literatureAn international cohort study of breast cancer survival in young women.PMC12923670Ginsburg ONarod SChitapanarux ITryggvadottir LAkbari MSopik VZendehdel KPongnikorn DLubinski JHuzarski TSripan PSun PVirani SGronwald JNahvijou AVatanasapt PCybulski CSriplung HfalseAn international cohort study of breast cancer survival in young women.<h4>Background</h4>There is large variation in case-fatality rates of breast cancer in young women across the world. The objective of this study was to estimate the ten-year overall survival of women diagnosed with breast cancer before age 40 in six countries, by clinical presentation and by treatments received.<h4>Methods</h4>Data were supplied by seven centers in six countries, including the USA, Canada, Poland, Iceland, Iran and Thailand, totaling 36,861 women diagnosed with breast cancer before age 40, from 1977 to 2020. American patients from the SEER registry were sub-divided into (Non-Hispanic) White and Black. The following factors were compared across countries: year of diagnosis, tumor size, lymph node status, estrogen receptor (ER) status, use of chemotherapy, use of tamoxifen a2026-01-01T00:00:00Z2026 Feb2026-07-16T14:53:27.119Z2026-07-09T11:01:08.28ZS-EPMC129236704172103310.1038/s44276-026-00207-z