Our body’s immune system is usually very good at spotting and clearing away old or damaged cells that may potentially develop into cancer, but sometimes these cells manage to stay hidden and proliferate in the body undetected. In some cases, the immune system may detect cancer cells but still need help eliminating them.
This is where immunotherapy comes in.
Medical oncologist Dr. Hsieh Wen Son delves deeper into the topic of immunotherapy, explaining the different types of immunotherapy, what it is used for, possible side effects and more.
When your body detects a substance that appears foreign, such as bacteria or viruses, your immune system raises an alarm and launches an immune response against it. However, there are limits to an immune system’s ability to destroy cancer cells.
This may happen when the cancer cells are too similar to normal cells, tricking the immune system into not recognising them as foreign, or if the immune response is not strong enough to destroy the cancer, or perhaps the cancer cells are giving off signals that help them hide from the body’s natural defenses.
Immunotherapy helps your immune system overcome these challenges. Dr. Hsieh explains that immunotherapy is based on a simple but powerful concept: teaching the immune system to identify cancer as a threat.
“Immunotherapies are essentially treatments that stimulate a patient’s immune system to attack the tumor,” Dr. Hsieh says.
Dr. Hsieh adds that immunotherapy offers hope to patients with previously untreatable cancers, like leukemia, lymphomas, and myelomas.
“We're curing patients with stage 4 lung cancer and stage 4 melanoma with immunotherapies,” Dr. Hsieh says. “Before immunotherapy, that was completely unheard of.”
There are several types of immunotherapy currently used in cancer treatment. Each type of immunotherapy works differently, but they all share the same goal: to harness the immune system’s ability to identify and destroy cancer cells.
One of the most widely used forms is known as immune checkpoint inhibitors. According to Dr. Hsieh, cancer cells often use certain “checkpoints” in the immune system as a way to disguise themselves.
“These checkpoint inhibitors basically take the mask off the cancer cells so the immune system can recognise them as harmful and attack them,” he explains.
Another form of immunotherapy is bispecific T-cell engager (BiTE) therapy. These therapies act like a bridge, linking immune cells directly to cancer cells so they can interact more effectively.
Chimeric antigen receptor (CAR) T-cell therapy is another highly advanced form of immunotherapy. In this treatment, immune cells are removed from the patient’s body and genetically modified in the laboratory to better recognise cancer cells. The modified cells are then returned to the patient, where they seek out and destroy the cancer.
Dr. Hsieh compares these engineered immune cells to “smart bombs” or “homing missiles” that are specifically trained to target cancer cells.
Immunotherapy has been described as one of the biggest breakthroughs in modern oncology because of its ability to produce long-term remission and even cure certain advanced cancers that were once considered untreatable.
“We’ve been waiting for immunotherapy for many years,” Dr. Hsieh says. “When the first examples came online, they were revolutionary.”
In the past, patients with stage 4 cancers such as melanoma often had very poor survival rates. Today, some patients treated with immunotherapy remain cancer-free even 10 years after treatment.
Dr. Hsieh explains that this may be because the immune system develops a form of memory after being trained to recognise the cancer, similar to how vaccines help the body remember infections.
“This is the same concept,” he says. “We are stimulating the immune system to attack the tumor, and one of the benefits is that the effects can be very long-lasting.”
Although not every patient experiences such outcomes, immunotherapy has significantly improved survival rates in selected cancers and continues to expand into more areas of cancer treatment.
Although chemotherapy and immunotherapy are both used to fight cancer, they work very differently. The primary distinction lies in how they target cancer cells and their mode of action.
With immunotherapy, the cancer cells are not targeted directly. Instead, it stimulates the immune system to recognise and attack the cancer cells more effectively. Chemotherapy, on the other hand, uses drugs that are toxic to rapidly dividing cells, including cancer cells.
These drugs work by interfering with DNA replication or the metabolic processes of cancer cells.
The effectiveness of these treatment methods varies based on the type of cancer, its stage and the patient’s specific health condition. Immunotherapy can more selectively target certain cancers, although its effectiveness varies between patients and cancer types. Chemotherapy can quickly shrink tumors, but because it also affects healthy rapidly dividing cells, side effects are more common.
Immunotherapy may be administered alongside chemotherapy and other treatment methods such as radiotherapy and surgery for better treatment outcomes. This combination may help enhance the body’s ability to fight cancer and render the tumor more susceptible to immune attacks.
Compared to chemotherapy and radiotherapy, immunotherapy generally causes fewer side effects because it works more selectively through the immune system. However, side effects can still occur.
In some cases, the immune system may become overly active and start attacking healthy organs and tissues in addition to cancer cells.
“We can’t always control the immune system completely,” Dr. Hsieh says. “Sometimes it becomes too active and attacks normal organs as well.”
Doctors manage these side effects using medications that suppress or slow down the immune response when necessary. While severe complications are less common than with traditional cancer treatments, careful monitoring of the patient’s condition remains important as side effects can occur unpredictably. In some cases, side effects may only appear weeks or even months after treatment has ended.
Today, immunotherapy is widely used around the world, including in Singapore. Although cost remains a challenge for some patients, Dr. Hsieh notes that increasing competition and the development of more treatment options are gradually helping improve accessibility.
Researchers continue to explore new forms of immunotherapy, different combinations of treatments, and better ways to identify patients who are most likely to benefit from this form of treatment.
While immunotherapy may not be a cure for every type of cancer, it has undeniably transformed treatment outcomes for many patients and opened up entirely new possibilities in cancer care.
“It doesn’t work for everyone, but it benefits many patients across different cancers and clinical situations,” Dr. Hsieh says.
