Abnormally high levels of P-cadherin – an adhesion molecule that enables cells to bind together – occur in about a third of all breast cancers and are associated with poor prognosis. Portuguese researchers , writing in the journal Oncogene1, found that the reason why these cancers are more aggressive is because excessive P-cadherin changes the cancer cells’ internal organization, making them mobile and invasive (invasiveness is the capacity to cross biological barriers such as membranes). Both these characteristics allow the formation of metastases - which is the spread of cancer cells from the original site of the tumour to other parts of the body - increasing the disease aggressiveness and explaining the poor prognoses associated with P-cadherin.