Immunotherapy in Cancer: How It Works
- , by SANUSq Research team
- 8 min reading time
One of the most exciting shifts in modern cancer treatment is the move to enlist the body's own immune system in the fight — an approach known as immunotherapy.
Cancer immunotherapy has moved from experimental to mainstream in recent years, transforming outcomes for some patients. This is a plain-English explainer of how it works and the main types — useful context whether you're simply curious or supporting someone through treatment.
How does immunotherapy work?
Your immune system is built to spot and destroy foreign threats — bacteria, viruses — by recognising unfamiliar proteins (antigens) on them. Cancer is harder for it to tackle, for two reasons. First, cancer cells arise from your own healthy cells, so the immune system doesn't always see them as "foreign". Second, many cancers actively evade or switch off the immune response. Immunotherapy works by tipping the balance back — either boosting the immune system's overall activity, or helping it specifically recognise and target cancer cells.
The main types of cancer immunotherapy
Monoclonal antibodies are lab-made proteins designed to attach to a specific target on cancer cells — flagging them for the immune system, blocking a growth signal, or delivering a payload directly to the tumour.
Checkpoint inhibitors are among the biggest breakthroughs. The immune system has natural "checkpoints" that stop it attacking healthy tissue; some cancers exploit these to switch off the immune response. Checkpoint inhibitors release that brake, freeing T cells to attack. Drugs targeting the PD-1 checkpoint, such as pembrolizumab and nivolumab, are now used across many cancers — including melanoma, non-small-cell lung cancer, kidney cancer, head-and-neck cancers and Hodgkin lymphoma.
Adoptive cell therapy (including CAR-T) takes a patient's own T cells, re-engineers them in the lab to recognise cancer, multiplies them, and returns them to the body as a living therapy.
In a pivotal international trial, the CAR-T therapy tisagenlecleucel produced an overall remission rate of 81% within three months in children and young adults with relapsed or refractory B-cell acute lymphoblastic leukaemia — a group with previously poor outlooks — though with serious, mostly reversible side effects (Maude et al., 2018).
Cytokines — immune-signalling chemicals such as interleukin-2 and interferon-alfa — can be given to rev up the immune response; lab-made IL-2 has been used in melanoma and advanced kidney cancer.
Cancer vaccines aim to train the immune system to recognise cancer. Most are still experimental, though sipuleucel-T (Provenge) is approved for certain advanced prostate cancers.
Why it suits some cancers and not others
One of the commonest questions is why a treatment that transforms outcomes for one person is never offered to another. Much of the answer lies in how visible a tumour is to the immune system in the first place.
Cancers arise through mutations, and each mutation can change a protein slightly. Some of those altered proteins look unfamiliar enough for T cells to recognise them, which gives the immune system something to aim at. Tumours carrying many such changes — melanoma and some lung cancers among them — tend to be more visible in this way. Others carry few, or sit in surroundings that keep immune cells out altogether; these are sometimes described as immunologically "cold", and releasing a brake achieves little if there were no T cells inside the tumour to release.
This is why tissue from a biopsy is often tested before immunotherapy is considered. Laboratories look for features that predict whether a particular drug is likely to work, such as how much of a checkpoint protein a tumour displays, or whether it carries a specific pattern of DNA-repair faults. Those results, alongside the cancer type, its stage, previous treatments and a person's general health and other conditions, are what an oncology team weighs up when deciding whether immunotherapy has a realistic chance of helping.
Immunotherapy side effects
Because immunotherapy ramps up the immune system, its side effects differ from those of chemotherapy. The main risk is that an over-active immune system starts attacking healthy tissues — so-called immune-related adverse events, which can affect the skin, gut, lungs, liver, or hormone-producing glands, and range from mild to serious. CAR-T and some other therapies can trigger cytokine release syndrome, a sometimes severe reaction with high fever and flu-like symptoms that usually needs hospital management. These risks are why immunotherapy is delivered and closely monitored by specialist teams.
Reporting side effects early
Two features of immune-related side effects make them different to live with. They can begin some weeks or months after treatment starts rather than straight away, and they can appear after a course has finished, so a symptom is not dismissed simply because the last infusion was a while ago. They also tend to be more manageable when caught early, which is why oncology teams put so much weight on being told promptly.
People having immunotherapy are usually given an alert card and a round-the-clock contact number, and asked to make contact about new or worsening symptoms rather than waiting for the next appointment — persistent diarrhoea, a spreading rash, breathlessness or a new cough, unusual tiredness, or anything else that feels out of the ordinary. Blood tests between cycles are part of the same watchfulness, since some effects on the liver, kidneys or thyroid show up in results before anyone feels unwell. When an immune-related reaction does occur, treatment is usually paused and medicines that damp the immune response, such as corticosteroids, are used to bring it under control.
Where immunotherapy fits
Immunotherapy is genuinely transforming care for some cancers, but it isn't right for every patient or every tumour type, and it's often used for advanced or hard-to-treat cancers, sometimes alongside other treatments. If it's being considered for you or a loved one, your oncology team is the best source of guidance on whether it fits your situation.
Frequently asked questions
How does cancer immunotherapy actually work?
It helps your own immune system fight cancer — either by boosting its overall activity or by helping it specifically recognise cancer cells it would otherwise miss. Different types do this in different ways, from releasing immune "brakes" to engineering a patient's T cells to hunt cancer.
What are the side effects of immunotherapy?
The commonest are immune-related adverse events, where the revved-up immune system inflames healthy tissues such as skin, gut, lungs or glands. Some cell therapies can cause cytokine release syndrome, a flu-like reaction that can be severe. Specialist teams monitor closely for these.
Is immunotherapy a cure for cancer?
It has produced remarkable, sometimes durable responses in certain cancers, but it isn't a universal cure — results vary by cancer type and patient, and it doesn't work for everyone. It's one powerful tool among several in modern oncology.
Who can have immunotherapy?
Eligibility depends on the cancer type, its molecular features, and the individual's overall health. It's frequently used for advanced or treatment-resistant cancers. An oncology team determines whether it's appropriate in each case.
How is immunotherapy different from chemotherapy?
Chemotherapy acts on the cancer cells themselves, targeting rapidly dividing cells. Immunotherapy acts on the immune system instead, helping it recognise and attack the cancer. That difference shows up in the side effects: chemotherapy's come largely from damage to fast-dividing healthy tissue, while immunotherapy's come from an immune system that has become over-active.
How long does immunotherapy treatment last?
There is no single answer. It depends on the drug, the cancer, how well it is working and how well it is tolerated, and cell therapies such as CAR-T work quite differently from repeated infusions. Your oncology team will explain the intended plan and review it as they go.
References
- Maude SL, Laetsch TW, Buechner J, et al. Tisagenlecleucel in Children and Young Adults with B-Cell Lymphoblastic Leukemia. N Engl J Med. 2018;378(5):439–448. PMID 29385370
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