Breast cancer patients could be encouraged to cut asparagus and other foods from their diets in the future to reduce the risk of the disease spreading, scientists say.
Researchers are investigating whether a change in diet could help patients with breast tumours after studies in mice showed that asparagine, a compound first identified in asparagus but present in many other foods, drives the spread of the disease to other organs.
When scientists reduced asparagine in animals with breast cancer, they found that the number of secondary tumours in other tissues fell dramatically. The spread of malignant cells, often to the bones, lungs and brain, is the main cause of death among patients who are diagnosed with breast cancer.
“This is a very promising lead and one of the very few instances where there is a scientific rationale for a dietary modification influencing cancer,” said lead scientist Prof Greg Hannon, director of the Cancer Research UK Cancer Institute in Cambridge.
Asparagine is an amino acid that is made naturally in the body as a building block for proteins. But it is also found in the diet, and in high levels in certain meats, vegetables and dairy products.
The international team of cancer specialists from Britain, the US, and Canada studied mice with an aggressive form of breast cancer. The mice develop secondary tumours in a matter of weeks and tend to die from the disease within months.
Writing in the journal Nature, the researchers describe how they reduced the ability of breast cancer to spread in the animals by blocking asparagine with a drug called L-asparaginase. To a lesser extent, by putting the animals on a low-asparagine diet worked too. Inspired by the results, the scientists examined records from human cancers and found that breast tumours that churned out the most asparagine were most likely to spread, leading patients to die sooner. The same was seen in cancers of the head, neck and kidney.
Asparagine appears to help cancer cells change into a form that easily spreads from the breast, through the bloodstream, to other organs where they grow into secondary tumours, Hannon said. While suppressing levels of asparagine reduced the spread of breast cancer around the body, it did nothing to prevent breast tumours forming in the first place.
If the findings hold in humans, breast cancer patients may be put on low asparagine diets while they have conventional treatments, such as chemotherapy, for the disease. But because asparagine is so ubiquitous in food, drugs that target the amino acid may be more effective. L-asparagine breaks the amino acid down in the bloodstream, but more targeted drugs could block its production altogether.
“This is one case where we can show at a deep biochemical level how a change in diet can impact properties of cells that are relevant to the progression of lethal disease,” said Hannon. “But of course, until human studies are done, this isn’t a DIY method to prevent cancer.”
Prof Keqiang Ye, a cancer researcher at Emory University in Atlanta, said that lowering asparagine levels, either with drugs or dietary restriction, would help prevent cancer cells from spreading. But for patients, he said that drug treatments held more promise than changes to their diets.
“Asparagine is frequently found in various animal sources including beef, poultry, eggs, fish and seafood. It is also found in many vegetables including asparagus, potatoes, nuts, legumes and soy. Since these foods are so common, it seems that diet restriction may not be the ideal approach,” Ye said.
Baroness Baroness Delyth Morgan, chief executive of Breast Cancer Now, said: “This early discovery could offer a long-awaited new way to help stop breast cancer spreading – but we first need to understand the true role of this nutrient in patients. With nearly 11,500 women still dying from breast cancer each year in the UK, we urgently need to stop the disease spreading around the body, where it becomes incurable.
“On current evidence, we don’t recommend patients totally exclude any specific food group from their diet without speaking to their doctors. We’d also encourage all patients to follow a healthy and varied diet – rich in fruit, vegetables and pulses, and limited in processed meat and high fat or sugar foods – to help give them the best chance of survival.”
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