Targeted therapy is able to shrink some tumours, making them removable by surgery and saving the lives of some patients with Stage 4 colon cancer. JUNE CHEONG reports

Although surgery is the traditional mainstay when it comes to treating colorectal cancer, other treatments include chemotherapy and targeted therapy.

These other treatment options can sometimes make a difference between life and death by shrinking previously inoperable tumours until they are able to be removed surgically.

Colorectal cancer refers to colon cancer, which forms in the tissues of the colon, or rectal cancer, which forms in the last six inches of the colon close to the anus. It is the most common cancer among men and
second most common cancer among women in Singapore.

Between 2003 and 2007, about 1,400 people here were diagnosed with the cancer each year.

Dr Wong Seng Weng, the medical director and consultant medical oncologist and physician at The Cancer Centre in Paragon Medical Centre, said that targeted therapy, together with chemotherapy, is
currently used to treat only Stage 4 colon cancer.

He said: “It increases the probability of shrinking the tumour and prolongs the patient's lifespan. I have had patients whose colon cancer had spread to much of the liver, making complete surgical removal of the cancer impossible.

“But by combining targeted therapy with chemotherapy, I could shrink the tumours in their livers and the patients could then undergo surgery. This effectively changed their fate from incurable to curable."

Professor Eu Kong Weng, the head and senior consultant surgeon at the department of colorectal surgery at Singapore General Hospital, said that those with Stage 1 or 2 colorectal cancer can usually be treated with surgery alone. Those with Stage 3 colorectal cancer are usually treated with surgery followed by chemotherapy.

The five-year survival rate for those with Stage 1 colorectal cancer is 90 to 95 per cent. The survival rate steadily declines across the stages to between 5 and 10 per cent for those with Stage 4 cancer.

When a patient reaches Stage 4, his treatment options usually span a combination of surgery, chemotherapy or targeted therapy.

Targeted therapy fights cancer by turning off the growth switch in colon cancer cells. This growth switch enables the colon cancer cells to grow and multiply.

However, there are some colon cancer types which are resistant to targeted therapy. Dr Wong said: “Certain colon cancer types carry a mutation in a particular gene, known as K-ras, that allows it to continue to generate the growth signal despite blockade of the growth switch."

To ensure that targeted therapy is appropriate and effective, doctors now test for such mutations in colon cancers before deciding whether or not to prescribe targeted therapy.

Another way in which targeted therapy fights cancer is by cutting the cancer cells' blood supply off.

Dr Wong said: “Cancer cells, like other cells of the body, cannot grow without a blood supply.

“Cancer stimulates new blood vessels to form and feed them by secreting a growth substance into the blood stream."

Researchers thus worked on synthesising an antibody which destroys the growth substance secreted by the cancer.

The resultant antibody disrupts the cancer's blood supply, thereby arresting the cancer's growth.