Targeted therapy is a new treatment that uses drugs to home in on cancer cells without destroying the patient’s normal cells. JUNE CHEONG reports

Fighting cancer may be akin to a long-drawn battle but doctors now have new weaponry that promises sweet victory for patients.

Called targeted therapy, this new type of cancer treatment uses drugs or other compounds to identify and attack cancer cells.

Dr Wong Seng Weng, a consultant medical oncologist and physician at The Cancer Centre in Paragon Medical Centre, said: “Drugs in targeted therapy are smart in the sense that they home in on the cancer cells and destroy them while avoiding injury to normal cells.”

Targeted therapy works by disrupting cancer growth and spread.

Most such drugs zero in on proteins involved in cancer cell signalling pathways, which govern cell functions and activities. These drugs may block signals which otherwise tell cancer cells to grow and divide incessantly.

They are also potent because they can cause cancer cell death while stimulating the immune system to recognise and attack cancer cells. They can also send toxic substances into cancer cells.

Such therapies usually come in the form of either small-molecule drugs or monoclonal antibodies.

The former are often able to enter cancer cells and act on targets inside the cell while the latter usually work on targets outside cancer cells or on their surfaces.
 
Asked about the advantages that targeted therapy has over conventional chemotherapy, Dr Wong said: “Chemotherapy has made impressive advancements over the years but its drawback still is that it damages not only cancer cells, but also normal cells of the body.

“More potent combinations of chemotherapy, therefore, often carry with them more severe side effects.

“Targeted therapy has the ability to home in and destroy cancer cells while sparing the normal cells.”

However, for now, while targeted therapy is invaluable in the war on cancer, its uses are still quite limited.

Dr Chin Tan Min, a consultant in the haematology-oncology department at the National University Cancer Institute, Singapore, said: “We know now that targeted therapy works best in cancers which display heavy dependence on specific pathways for their growth.

“When these growth signals are blocked by targeted therapy, the cancer’s growth is arrested. Often, good tumour control results.

“The challenge remains in defining the Achilles’ heel of various cancers since different cancers may display different types of pathway dependence.”

Meanwhile, to attain a small-molecule drug, thousands of test compounds are identified and tested before one or a few are chosen and chemically modified to create the most effective and specific drug.

Monoclonal antibodies are made by testing antibodies against target molecules introduced in animals, usually mice, and then cultivating and modifying the effective antibodies in the laboratory.

A particular targeted therapy may be used alone in cancer treatment or combined with conventional chemotherapy or other targeted therapies.

Targeted therapy is currently used to treat different types of cancer like that of the breast, lung and colon. In future, it is expected to help doctors specially tailor cancer treatments to each individual patient.

However useful targeted therapy is, it cannot win the day entirely. It has been found that cancer cells have the potential to develop resistance to it.

The fight against cancer still lies in the array of weapons at an  oncologist’s disposal.

Dr Wong gave this analogy: “Just because we have a smart bomb does not mean that we no longer need soldiers and tanks.

“But the availability of a smart bomb that accurately hits high value enemy targets will vastly increase the odds of winning the battle.

“For instance, targeted therapy may be used to deprive a cancer of its blood supply, thus arresting cancer growth, while chemotherapy works to kill off the cancer cells.”