HK scientists find stem cells causing spread of colon cancer, offering treatment hope

Hong Kong scientists have for the first time identified cancer stem cells responsible for spreading colorectal cancer, a discovery that could bring better-targeted treatment of the city's second deadliest malignancy.

The University of Hong Kong team of molecular biologists was able to show that if the two stem cells were injected into specially bred mice, the colorectal cancer spread to the liver.

The team is also the second in the world to show evidence that specific stem cells trigger the growth of colorectal cancer.

Stem cells can grow into any organ but some researchers believe that rogue stem cells could be seeding some, if not all, cancers.

These cancer stem cells are now the focus of intense global research as some patients do not respond well to chemotherapy or if the cancer returns in a more aggressive form.

'[Colorectal cancer] is one of those cancers with a well-established treatment regimen but it remains the second cause of cancer death in Hong Kong, suggesting that the current therapies are not adequate to cure the disease,' said Roberta Pang Wen-chi, research assistant professor at the university's department of medicine, who is lead investigator.

Dr Pang said her team and scientists at the Ontario Cancer Institute at Princess Margaret Hospital in Toronto might have been studying the same stem cell protein - CD133 - at the same time last year, but it was the Canadian team that published the breakthrough first in the journal Nature. The Hong Kong study would be submitted to an international journal by the end of the month.

'We started to look for other markers or proteins on the surface of stem cells,' she said. 'The novelty of our research is the metastatic part.'

Metastasis is the process by which cancer spreads from where it first arose to other locations in the body.

The Hong Kong team extracted cancer tissues from 30 patients and isolated the cancer stem cells, which were implanted into the colons of about 120 immune-deficient mice.

For the growth of primary colorectal cancer, the team identified two proteins, CD133 and CD44. The team also found CD133 and CD26 initiated the spread of colorectal cancer to the liver. CD133 has also been implicated in the growth of cancers of the brain and breast.

'We showed that they not only grow but they can actually metastasise to the liver. This is the first time it has been shown in animal models. Usually in animal models it is not easy to show metastasis with these stem cells,' Dr Pang said.

'We believe these stem cells have the ability to self-renew, so we believe these cells are responsible for tumour maintenance and metastasising. They are more resistant to chemotherapy,' she said.

The next step would be to look for colorectal patients who were resistant to chemotherapy and see whether 'they have high expressions of these cancer stem cells'.

Battling a killer

The incidence of colorectal cancer has risen by over 10 per cent in the past decade

The number of new colorectal cancer cases in 2005: 3,706

Source: Hong Kong Cancer Registry (latest figure)