Risk assessment and genetic testing for breast cancer are at the vanguard of a rapidly expanding field of medicine, while the molecular genetics of breast cancer is a focus for a growing field of basic and applied scientific research. The last decade has also seen an exponential rise in health 'activism' around breast cancer. Using an ethnographic approach, Sahra Gibbon examines the relationship between these seemingly parallel developments. She draws on research in two contrasting social arenas - cancer genetic clinics and a breast cancer research charity - exploring the collective practices, networks and identities caught up in the translation of genetic knowledge from, to and between the laboratory and the wider world. She points to a powerful social form within the so called 'new ' genetics that aligns gender with the knowledge and technologies associated with breast cancer genes, whilst also showing how the circuits of connection between people and practices in different social arenas operate in complex and non-linear ways.