BRCA1 and breast cancer: The segregation model estimates the hazard function hG(t | x1) at age t due to genetic factors, conditional on information (denoted x1) about a woman’s family history (family tree) of breast and/or ovarian cancer, and results of any tests in the family from known highly penetrant breast cancer genes BRCA1 and BRCA2. This is then combined with a relative hazard regression function r(x2) > 0 based on other risk factors (x2) through (4)h1(t|x1,x2)=hG(t|x1)r(x2).