A website has been published which allows the user to enter information on prognostic factors for a patient with breast cancer, and instantly obtain a survival curve based on outcome data of prior cases with a matching prognostic factor profile. The source for the survival data is a Finnish nationwide series (the FinProg series) of 2,842 women diagnosed with breast cancer in 1991-2. The purpose of this study was to compare survival estimates based on the FinProg database, with estimates for breast cancer patients from the US, obtained from the SEER public-use database and the same time period. Results show that a reasonable level of agreement between estimates can be reached, by the use of large, unselected databases, and that significantly different estimates were obtained in only 2 of 19 analyzed prognostic profiles. The current system could be used to share important knowledge on outcome between researchers and clinicians at different institutions, and be used in the decision-making process concerning treatment of patients with breast cancer.