Prof Jordan talks to ecancertv at the World Oncology Forum 2015 about how tamoxifen - a drug originally developed as a contraceptive - has gone on to become an effective breast cancer drug.
However, he argues that tamoxifen isn't worth taking as a preventive measure against breast cancer and that we need 'smarter' medicine.
He explains how many drugs effective in treating breast cancer have other effects on the body which can be good or bad depending on the individual. He explains the undesirable impacts of some drugs which helped against breast cancer but contributed to endometrial cancer.
On the other hand, some breast cancer drugs, such as lasofoxifene (which he describes as a "miracle of molecular biology"), can prevent stroke, osteoporosis and heart disease.