Using tumour morphology data collected by a standard pathology review of many of the breast cancers arising in women participating in the Australian and Ontario BCFRs, and by performing an extended review of the medullary and atypical medullary type breast cancers in the northern California BCFR (see Materials and methods), we identified 133 women whose tumour morphology met our selection criteria and thus had many of the morphological features consistent with being a BRCA1 mutation carrier. The gene discussed is BRCA1; the disease is breast cancer.