This window could one day play a big role in analysing how well developmental drugs block cancer from spreading, said Dr Jeffrey Segall, a researcher at the Albert Einstein college of Medicine of Yeshiva University in New York.

'We hope this technology can be used to test the ability of various drug treatments to inhibit tumour cell invasiveness and metastasise,' said Dr Segall, who led the study. 'In addition, the technology may be useful for following drug effects on tumour growth.'

A single tumour is easier to treat but many times cancer cells metastasise by entering the bloodstream and spreading to other parts of the body. This is far more dangerous and what mainly kills people with the disease, Dr Segall added.

So, better understanding this process by tracking cancer cells as they spread in the laboratory is an important step in more effectively treating the disease, Dr Segall said.

'What we saw is that tumour cells invade in different amounts depending on where they are in the tumour,' Dr Segall said. 'The most invasive ones are the ones around the blood vessels.'

There have been previous indications this is the case, and the study published in the journal Nature Methods appears to confirm this,Dr Segall added in a telephone interview.

To do this, the researchers implanted a little glass window in the skin of the mouse over the mammary gland and attached it with sutures about 3 millimetres to 5mm across. The mice were injected with a breast cancer.

Then they used the same glowing jellyfish protein technique that won this year's Nobel Prize in Chemistry to illuminate the cancer cells under ultraviolet light to better track the tumours, Dr Segall said.

'The window allows us to look at the tumour over multiple days and the marking allows us to find those cells,' Dr Segall said. 'We can track for longer periods and more easily.' -- REUTERS