The deadly spread of cancer around the body has been cut by three-quarters in animal experiments, say scientists.
Tumours can "seed" themselves elsewhere in the body and this process is behind 90% of cancer deaths.
The mouse study, published in Nature, showed altering the immune system slowed the spread of skin cancers to the lungs.
Cancer Research UK said the early work gave new insight into how tumours spread and may lead to new treatments.
The spread of cancer - known as metastasis - is a fight between a rapidly mutating cancer and the rest of the body.
The team at the Sanger Institute in Cambridge was trying to figure out what affected tumour spread in the body.
Researchers created 810 sets of genetically modified lab mice to discover which sections of the DNA were involved in the body resisting a cancer's spread.
The animals were injected with melanomas (skin cancer) and the team counted the number of tumours that formed in the lung.
Their hunt led them to discover 23 sections of DNA, or genes, that made it either easier or harder for a cancer to spread.
Many of them were involved in controlling the immune system.
Targeting one gene - called Spns2 - led to a three-quarters reduction in tumours spreading to the lungs.