Therefore, we undertook a study to 1) determine the prevalence of loss of heterozygosity with loss of the wt BRCA1 allele in ER+ cancers from BRCA1 mutation carriers and compare it to that found in ER- BRCA1-associated cancers; and 2) determine whether any clinical factors (that is, age at diagnosis), pathologic features or biomarkers predict for loss of wt BRCA1 in BRCA1-associated breast cancers. The gene discussed is BRCA1; the disease is breast cancer.