BRCA1 and cancer: The majority of families carrying rare mutations were not detected through sequencing a prospectively demonstrated cancer case: In the files at The Norwegian Radium Hospital which was available for detailed analysis, 547 women in 127 different kindreds were identified to have rare BRCA1 mutations, while the number of prospectively detected cancers in women with no cancer prior to or at first control and with rare BRCA1 mutations not included in the test panel used for all families, was 24.