Jim Al-Khalili talks to breast cancer pioneer, Professor Valerie Beral director of the cancer epidemiology unit in Oxford about her Million Women study and why she thinks a so-called 'vaccine' should be developed to prevent breast cancer. Jim finds out why the brilliant mathematician who became female Australia junior chess champion as a teenager and who got a first class degree in medicine decided she was unhappy with the uncertainties of diagnosis as a doctor, and turned her back on clinical medicine in the quest for answers to the bigger questions about public health. She talks about pioneering research into the causes of cancer, effects of the contraceptive pill, radiation from Chernobyl and Hiroshima. Most recently as lead investigator on the million women study she has looked at the risks and health effects from taking HRT. She has said that it is a 'crime' that more research hasn't been done on what is known about women who don't get breast cancer to prevent breast cancer in other women.