Immunotherapy and chemotherapy are both important cancer treatments, but they work in fundamentally different ways. Chemotherapy uses medicines that directly kill cancer cells or stop them from growing, while immunotherapy helps the immune system recognise and fight cancer. Depending on the cancer, these treatments may be used separately or together.
If you are trying to understand where immunotherapy fits into cancer care, our Cancer Immunotherapy guide provides a broader overview of how these treatments work and when they may be considered.
Understanding the difference between immunotherapy and chemotherapy can make treatment discussions easier, particularly when both options are being considered. Neither treatment is universally suitable for every cancer or every patient. The choice depends on factors such as the type and stage of cancer, tumour characteristics, previous treatment and overall health.
Immunotherapy vs Chemotherapy at a Glance
| Feature | Immunotherapy | Chemotherapy |
|---|---|---|
| Primary approach | Helps the immune system recognise and attack cancer | Directly kills cancer cells or stops their growth and division |
| Main target | Immune response and mechanisms that help cancer evade it | Cancer cells, particularly rapidly dividing cells |
| Effect on healthy cells | Can cause inflammation when an activated immune system affects healthy tissues | Can affect healthy cells that divide rapidly |
| Response pattern | Can sometimes take time to become apparent | Response is generally assessed through tumour measurements, symptoms and other tests |
| Duration | Varies according to the drug, cancer and response | Often given in treatment cycles with periods of recovery |
| Can they be combined? | Yes. Some cancer treatment plans combine immunotherapy with chemotherapy. | |
How Does Chemotherapy Work?
Chemotherapy uses medicines that kill cancer cells or stop them from growing and dividing. Because many cancer cells multiply quickly, they can be particularly vulnerable to these medicines.
However, some healthy cells also divide rapidly. Cells in the hair follicles, mouth, digestive tract and blood-forming tissues can therefore be affected by chemotherapy. This helps explain why chemotherapy can cause side effects such as hair loss, mouth sores, nausea, changes in blood counts and increased risk of infection.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Chemotherapy can be used for different purposes. Depending on the cancer, it may be given before surgery to shrink a tumour, after surgery to destroy remaining cancer cells, alongside radiation therapy, or to control cancer that has spread or returned.
How Does Immunotherapy Work?
Immunotherapy takes a different approach. Rather than directly attacking cancer cells in the same way as chemotherapy, it helps the body's immune system recognise or respond to cancer more effectively.
One commonly used form is an immune checkpoint inhibitor. Checkpoint proteins normally help prevent the immune system from becoming excessively active. Some cancers use these pathways to avoid immune attack. Checkpoint inhibitors can block these signals and allow T cells to attack cancer cells more effectively.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Other forms of immunotherapy work in different ways, including certain monoclonal antibodies, immune system modulators and cellular therapies.
The Biggest Difference: Direct Attack vs Immune Response
The simplest way to understand the difference is to look at what each treatment is primarily trying to do. Chemotherapy acts directly on cancer cells and other rapidly dividing cells. Its effect comes from the drug reaching the cancer and interfering with processes needed for cell growth or survival.
Immunotherapy works through the immune system. The treatment may remove signals that suppress immune activity, strengthen immune responses or provide immune cells with a greater ability to recognise cancer. This difference also helps explain why the two treatments can have very different side-effect patterns.
How Are the Side Effects Different?
Both treatments can cause side effects, but they do so for different biological reasons.
Chemotherapy Side Effects
Because chemotherapy can affect healthy cells that grow and divide quickly, common side effects may include:
- Hair loss
- Nausea and vomiting
- Mouth sores
- Fatigue
- Lower blood cell counts
- Increased risk of infection
- Changes in appetite or digestion
The exact effects depend on the chemotherapy drug or combination, dose and individual patient. Many chemotherapy side effects improve after treatment is completed, although some can persist or require longer-term management.
Immunotherapy Side Effects
Immunotherapy side effects can occur because the immune response activated against cancer also affects healthy tissues.
Common effects can include fatigue, rash and diarrhoea. In some patients, immune-related inflammation can affect organs such as the lungs, liver, intestines, kidneys, thyroid, heart or nervous system.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
These reactions are not inevitable, and many patients do not experience serious immune-related complications. However, new or worsening symptoms should be reported because some immune-related side effects require prompt treatment.
Does Immunotherapy Have Fewer Side Effects Than Chemotherapy?
It is not accurate to assume that immunotherapy is simply a less toxic version of chemotherapy. The side-effect profiles are different rather than one being universally easier.
Chemotherapy can cause effects related to damage to rapidly dividing healthy cells, while immunotherapy can trigger inflammation or immune reactions affecting healthy organs.
Some people may tolerate one treatment better than another, but individual experiences vary considerably. The specific medicines being used are also important because both chemotherapy and immunotherapy include many different drugs with different safety profiles.
How Quickly Do the Treatments Work?
The response pattern can differ between chemotherapy and immunotherapy, but there is no universal timeline for either treatment.
Chemotherapy can sometimes produce relatively rapid changes in tumour size because the medicines act directly on cancer cells. However, the speed of response depends on the cancer type, the drugs being used and how sensitive the cancer is to treatment.
Immunotherapy depends on activating or strengthening an immune response, so its effects may not always follow the same pattern as chemotherapy.
In some cases, the response can take time to become apparent. Doctors therefore assess treatment using scans, symptoms, physical examinations and other appropriate tests rather than judging effectiveness by how quickly a person feels different.
Can Immunotherapy and Chemotherapy Be Given Together?
Yes. Combining the two treatments is an established approach for several types of cancer. The reasoning is that the treatments can work through different mechanisms.
*AI-generated image - for illustration only. Clinical accuracy is not guaranteed.
Chemotherapy directly affects cancer cells, while immunotherapy can help the immune system respond to the cancer. In some treatment plans, using both approaches can provide a broader attack on the disease.
The combination is sometimes referred to as chemoimmunotherapy. Whether it is appropriate depends on the cancer type, stage, biomarkers and the specific treatment regimen being considered.
How Do Doctors Decide Between Immunotherapy and Chemotherapy?
The decision is based on the complete clinical picture rather than simply comparing the two treatments. Factors that may influence the treatment plan include:
- Cancer type: Different cancers respond differently to chemotherapy and immunotherapy.
- Stage: Treatment choices can change depending on whether the cancer is localised, locally advanced or metastatic.
- Biomarkers: Certain molecular or immune markers can help identify treatments that may be appropriate.
- Previous treatment: Earlier chemotherapy, radiation, targeted therapy or immunotherapy can influence what comes next.
- Overall health: Other medical conditions and the ability to tolerate treatment are important considerations.
- Treatment goals: The approach may differ when the goal is cure, reducing the risk of recurrence, controlling advanced disease or relieving symptoms.
How Is Treatment Response Monitored?
You cannot reliably tell whether either treatment is working simply by looking at its side effects. Some people experience significant side effects while their cancer responds well, while others may have few noticeable side effects despite the cancer progressing.
Doctors therefore use objective assessments to monitor treatment. Depending on the cancer, this may include imaging such as CT, MRI or PET scans, blood tests, physical examinations and assessment of symptoms. The timing and type of monitoring vary according to the treatment and cancer being treated.
The Bottom Line
Immunotherapy and chemotherapy are different approaches to treating cancer. Chemotherapy directly attacks cancer cells and can also affect healthy cells that divide rapidly. Immunotherapy works by helping the immune system recognise and fight cancer, which can produce a different pattern of side effects and treatment response.
Neither treatment is automatically the right choice for every patient. Depending on the cancer, they may be used separately, sequentially or together. Other treatments, including surgery, radiation and targeted therapy, may also form part of the overall plan.
The most useful question is therefore not simply whether immunotherapy or chemotherapy is “better,” but which treatment or combination of treatments fits the specific cancer, its biological characteristics, treatment history and the goals of care.
