US scientists have proved drinking alcohol when you have breast cancer fuels the growth of tumours.

It has long-been said alcohol increases the risk of developing cancer but the effect of drinking once cancer is present is less established.

A University of Mississippi team found mice given the equivalent of two to four drinks a day doubled the normal growth of a tumour after four weeks.

In the study, researchers gave female mice the human equivalent of two drinks a day for four weeks, while a control group were given no alcohol.

The mice were then injected with breast cancer cells.

Within four weeks, the tumours in the alcohol-fed mice weighed 1.4g on average, almost twice the size of tumours in the control group.

The team, which presented the research to the American Physiology Society, said alcohol caused cancer cells' blood vessels to grow which in turn fuelled the growth of the tumour.

The mouse study builds on an earlier research with chicks that showed alcohol consumption increased the expression of a protein known as VEGF, which fuels tumour growth by spurring the development of blood vessels in cancer cells that might otherwise die.

Normally, the immune system can kill off small tumours, but when they grow large enough the body can no longer fight off the tumour cells.

Lead researcher Jian-Wei Gu reported the vast majority of tumours result from over expressed VEGF, adding every day, the body produces a lot of cancer cells, but they don't become bigger.

But if the cells establish blood vessels, the tumour grows and strengthens, a process known as angiogenesis, the advice from the research team is patients should not drink if they were undergoing cancer treatment.

Cancer Research UK in a statement said the link between alcohol and breast cancer, and many other cancers, is well known.

"But this is the first time they have heard of the impact of alcohol once cancer is established, and as such more research was needed to see if the findings were replicated in adults and whether it also applied to other cancers.

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