Practical guide for estimating risk for familial breast cancer.

Life-table analysis was used to estimate the cumulative risk of breast cancer to various ages for mothers and sisters of breast cancer patients in a population-based series. These cumulative risk estimates were then used to derive a probability of breast cancer diagnosis within each decade between ages 20 and 70 for mothers and sisters, according to age of diagnosis in the patient and whether the disease was unilateral or bilateral. Risks for relatives of premenopausal patients with unilateral disease were no higher than those for relatives of postmenopausal patients. Relatives of premenopausal patients with bilateral disease had higher risk than relatives of patients with unilateral disease, irrespective of age at diagnosis in those with unilateral disease. Sisters were at higher risk than were mothers.