The 'Achilles heel' of cancer has been discovered by scientists - raising hopes of a cure.
It's a 'door' that allows chemicals to enter and leave cells. Shutting it stopped the disease in its tracks.
In experiments, aggressive tumours in mice shrank in size - leaving healthy tissue unharmed.
This was achieved by blocking proteins called 'nuclear pores complexes' - large channels that regulate the flow of materials in and out of a cell's command centre.
Lead author Professor Maximiliano D'Angelo, of Sanford Burnham Prebys Medical Discovery Institute in La Jolla, California, said: "Nuclear pore complexes are the 'doors' that all materials pass through to gain entry to the cell's nucleus.
"Because cancer cells are rapidly growing and dividing they need and create more nuclear pore complexes than normal cells.
"Our study is the first to demonstrate by blocking the formation of these nuclear 'doors' we can selectively kill cancer cells."
The researchers describe it as an 'Achilles heel'. The breakthrough 'opens the door' to better treatments for the deadliest forms.
Tumours grow and spread - or metastasise - through the transport of molecules through the nuclear pores.
The study, published in the journal Cancer Discovery, prevented the process. Prof D'Angelo's technique only targets dividing, cancerous cells - making it safe for humans.
His team transplanted human tumour cells unable to form nuclear pore complexes into the lab rodents.
Three different types were used - melanoma, leukaemia and bowel cancer - which are known to be especially reliant on these 'doorways'.
The scientists found that all of the mice had smaller tumours - and slower growth.
First author Stephen Sakuma, a graduate student in the D'Angelo lab, said: "We showed the inability to build nuclear pore channels is devastating for rapidly-growing cancer cells.
"But it doesn't seem to have an impact on healthy cells - which simply halt their growth and then recover.
"Our findings provide an important proof of concept this approach could lead to a new type of cancer treatment, which might be especially beneficial for aggressive or metastatic cancers that are difficult to treat."
Now it has been demonstrated the approach works, the researchers are trying to find a drug that can block the formation of nuclear pore complexes.
Attempts are ongoing at Sanford Burnham Prebys - one of the most advanced drug discovery centres in the non-profit world.
Prof D'Angelo said: "In addition to one day helping people with tough-to-treat cancers, we envision this drug candidate might be used to prevent drug resistance, which happens when tumours adopt properties to resist therapy.
"Tumours would have a hard time adopting to an environment where their 'doors' are removed, so this drug might help certain treatments, such as targeted therapies, remain effective for longer periods of time."
Cancer is the world's second biggest killer - behind cardiovascular disease. In 2018 it was responsible for an estimated 9.6 million deaths.
Globally, about one in six deaths is due to cancer. Most occur in low and middle income countries.