HKU scientists identify cancer stem cells

Scientists at the University of Hong Kong have homed in on the specific cancer stem cells that are responsible for the usually fatal spread of colorectal cancer to other organs.

The research finding, described as revolutionary, marks a paradigm shift in dealing with colorectal cancer. Current treatments regard all cancer cells homogenously and try to eliminate them all via chemotherapy or surgery.

'It will revolutionise the approach to cancer treatment in future,' said one of the researchers, Ronnie Poon Tung-ping, an HKU professor in surgery. 'If you just target mature cancer cells, you are not targeting the roots of the disease. What the industry needs to work on now is drugs that will target cancer stem cells.'

The breakthrough will allow doctors to predict high-risk patients whose cancers are liable to spread - in a process known as metastasis - accurately before it occurs.

Treatments can also be developed that specifically target these cancer stem cells, called CD26+.

Scientists do not know how CD26+ cells come about. Such cells are not only resistant to chemotherapy but can be enriched by the process. More than half of patients who undergo colostomies, where part of the colon is removed, still experience metastasis.

The study found that even when most of the cancerous cells were eradicated and the tumour appeared to shrink, it could take as few as 1,000 cancer stem cells for it to regrow. These cells can change into various cell types and drive the spread of tumours, sometimes exponentially.

The scientists found it was far more reliable to use CD26+ cells than carcinoembryonic antigens, which are proteins secreted by cancer cells, to predict metastasis.

They found a link between CD26+ cells in a patient's tumour and blood, which would help doctors detect cancer better. Patients in the early stages can thus seek intensive treatment long before metastatis begins.

Cases of colorectal cancer in Hong Kong are rising rapidly. In 2008, the city saw more than 1,680 deaths, or 13.5 per cent of all cancer deaths. The disease is set to become the city's most common cancer in the next few years, overtaking lung cancer.

Worldwide, colorectal cancer is the second most common cause of cancer-related death. Only 8 per cent of patients who suffered colorectal cancer with metastasis survived for at least five years. The disease usually spreads to the liver.

New cases in Hong Kong exceed 4,000 per year. Part of the reason is the popularity of high-fat, high-cholesterol fast food. 'Fat cells are also carcinogenic. So westernised diets, meaning high-fat diets, are actually carcinogenic,' said Dr Roberta Pang Wen-chi, research assistant professor in medicine at HKU and another of the study's scientists.

The study was featured last month on the cover of Cell Stem Cell, The publication is the highest-ranked journal for stem cell research, according to the professional and scholarly publishing division of the Association of American Publishers.

Cancer stem cell research is a relatively new field. 'Previous studies have been more focused on the tumour-initiating capacity rather than the metastatic capacity,' Pang said. 'I think this is the first study that actually showed that the stem cells can metastasise to another organ and that's the significance.'