Targeted therapies for colorectal cancer

With colorectal cancer on the rise in the city, it's time to get serious about prevention, writes Elaine Yau

PUBLISHED : Monday, 15 April, 2013, 12:00am
UPDATED : Monday, 15 April, 2013, 10:23am

With new cases of colorectal cancer more than doubling over the past decade, oncologists warn that it will soon become the top cancer killer in Hong Kong.

Figures from the Hospital Authority's Cancer Registry show there were 4,370 new cases in 2010, compared to 2,033 in 2000. This is a 115 per cent increase, which is a lot higher than the 13.4 per cent increase in new lung cancer cases over the same period.

While lung cancer still tops the incidence list with 4,480 new cases reported in 2010, specialist in clinical oncology Anthony Ying Chi-ho says colorectal cancer will become the most prevalent cancer in a few years' time.

He attributes the rising incidence to the spread of Westernised lifestyles among locals. "People's diets are composed of lots of meat and few vegetables," he says.

"It takes longer to digest meat. Overconsumption of red meat slows down bowel movement. Traces of toxins released by red meat or processed meat accumulate in the intestines, increasing the risk of colorectal cancer."

A survey conducted by the Hong Kong Anti-Cancer Society on 2,107 people last year showed how common poor diet and lack of exercise are among locals. Forty per cent of respondents were overweight, half did fewer than two hours of exercise per week and 30 per cent consumed 500 grams of red meat every week, the maximum amount considered safe by nutritionists. Thirty per cent also said they have less than one serving of vegetables per day on average.

Overconsumption of red meat slows down bowel movement. Traces of toxins released by red meat or processed meat accumulate in the intestines and increase the risk of colorectal cancer
Anthony Ying Chi-ho, oncologist

Ying says people should change their lifestyles and get screened regularly as colorectal cancer is preventable.

Those aged 50 to 75 who do not show any symptoms are considered to have a medium risk of developing the disease, he says, and should undergo annual fecal occult blood testing, a process that detects blood in stool samples that is not visibly apparent. Every five years, these people should have a sigmoidoscopy, which essentially examines the last 60cm of the large intestine, where 60 per cent of colorectal cancer cases are found. A colonoscopy, which examines the inside of the entire large intestine and rectum, should be done once a decade.

"If people display symptoms like anal bleeding or blood-tainted stools, drastic weight loss or stomach aches, they should seek medical help as soon as possible," says Ying.

Such symptoms are signs of late-stage cancer. Cancer Registry data shows that more than 20 per cent of colorectal cancer patients are diagnosed only at stage four, when the tumour has spread to other organs such as the lungs and liver. In 2010, 9.5 per cent of colorectal cancer cases were diagnosed at stage one, 25 per cent at stage two and 25.2 per cent at stage three.

Chan Leung-cho, a consultant oncologist with the Anti-Cancer Society's chemotherapy centre, says those whose family members have colorectal cancer are considered high risk. "They need to start testing 10 years before the age their relatives were stricken by the cancer," he says. If family members have a history of polyps - fleshy growths on the lining of the colon that may become cancerous - they should also get a check up.

"Surgical removal of polyps can prevent colorectal cancer," says Chan.

As researchers learn more about the gene and protein changes in cells that cause cancer, they develop new drugs to target these changes. These medicines often have different (and less severe) side effects compared to standard chemotherapy and offer the hope of control, and even cure, of cancer in stage four patients, says Chan. There are two targeted therapies for metastatic colorectal cancer: cetuximab (trade name Erbitxu) and bevacizumab (Avastin). Cetuximab can affect cancer cell growth by attacking the epidermal growth factor receptor (EGFR), a protein receptor that 90 per cent of metastatic colorectal patients possess. Bevacizumab is a drug that slows the growth of new blood vessels that provide cancer cells with nutrients and oxygen to grow. Both drugs are used in combination with standard chemotherapy.

About 40 per cent of colorectal cancer patients however are not able to take cetuximab as they have mutations in a gene called KRAS. Studies show that if the gene mutation is present, patients will respond poorly to anti-EGFR medications. Such patients should take bevacizumab so that unnecessary toxicity and financial cost can be spared.

Large-scale clinical studies show that chemotherapy combined with anti-EGFR targeted therapy produce a response rate double that of chemotherapy on its own. The treatment lasts six months, and after the tumour shrinks, it is removed. In the case of metastatic colorectal cancer that has only spread to the liver, more than 70 per cent of patients who received such therapy saw their tumour shrink by more than half. A third of such patients can eventually undergo surgery to get the metastatic tumour removed, increasing their survival by four to five years.