Because breasts are not critical to survival, cancers that remain within breast tissue do not kill the patient. But if the cancer cells break away from the original tumour, settle and start dividing elsewhere, these secondary tumours can threaten the function of vital organs. Rather like an invasive plant landing on an island, the circulating breast cancer cell needs to evolve genetic changes to survive in a new environment. It has to find a way to stick to a new type of cell or supporting structure, called a matrix, and form links to surrounding cells, for instance.
Now a protein has been found that changes the levels at which more than a thousand genes are expressed in breast cancer cells, seemingly controlling whether cancer cells will survive elsewhere. The protein is called SATB1. “All sorts of molecular pathways that enable the cell to invade and inhabit a new microenvironment are under the control of SATB1,” says Terumi Kohwi-Shigematsu of the University of California, Berkeley, who was an author of the study.