Affected families have several members with breast cancer or other cancers.
Inherited breast cancer usually shows itself early, often in the under-50s. One breast cancer gene has been isolated - testing for carriers may be possible for some affected families. A new life begins when a sperm fertilises an egg. From this single fertilised cell develop all the countless million different cells of an adult person. The blueprint for this remarkable feat of construction lies in the genes present in the original fertilised egg - half of which came from the mother, and were already in the egg, and half of which arrived, via the sperm, from the father.