A fatty molecule lays down a "breadcrumb trail" that allows malignant skin cancer to spread around the body, research has shown.
Signals from the molecule, lysophosphatidic acid (LPA), help to make melanoma cells unusually aggressive and mobile.
Scientists hope the discovery will lead to new strategies for slowing or halting the lethal spread of melanoma.
Tests on laboratory cell lines and mice revealed how the tumour cells start their journey by breaking down a nearby source of LPA.
Once those molecules are depleted, the cells move out of the tumour in search of more. Each encounter with LPA prompts the cells to keep moving.