Immunotherapy in cancer refers to treatment that harnesses, enhances, redirects or otherwise modifies immune responses so that the immune system can recognise and attack malignant cells. Unlike conventional chemotherapy, which directly targets cellular processes with cytotoxic medicines, many immunotherapies work by altering the relationship between tumour cells and immune cells. Cancer can evade immune destruction through mechanisms that suppress immune activation, alter antigen presentation, create an immunosuppressive microenvironment or exploit inhibitory signalling pathways.
Therapeutic strategies can counter some of these mechanisms. Important classes include immune checkpoint inhibitors, cellular therapies, monoclonal antibodies with immune-mediated effects, cancer vaccines and immune-modulating agents. The term is broad and encompasses treatments with substantially different mechanisms. Immunotherapy can produce durable responses in some cancers because immune memory and continued immune surveillance may persist after the treatment itself has been administered. However, response is not universal, and some tumours possess biological features that make them less visible or less vulnerable to immune attack. The clinical value of immunotherapy therefore depends heavily on tumour type, immune context and the specific mechanism of the treatment.
Immune checkpoint inhibitors are among the most important forms of Immunotherapy. T cells possess inhibitory pathways that help prevent excessive immune activation and damage to normal tissues. Tumours can exploit these pathways to suppress anti-tumour T-cell activity. Medicines that block inhibitory interactions involving CTLA-4 or PD-1 and PD-L1 can restore or enhance T-cell activity in appropriate circumstances.
Their effects are indirect in the sense that the drug does not necessarily kill the cancer cell itself; instead, it changes immune signalling so that existing immune mechanisms can attack the tumour. Some cancers respond particularly well to checkpoint blockade, while others show lower response rates. Biomarkers such as PD-L1 expression, microsatellite instability or mismatch-repair deficiency can provide information about the likelihood of benefit for selected cancers, but no single biomarker perfectly predicts response in every setting. Tumour mutation burden and other features of the tumour immune microenvironment may also be relevant. Checkpoint inhibition demonstrates why immunotherapy differs fundamentally from simply giving a medicine that is toxic to rapidly dividing cells.
Cellular Immunotherapy involves administering immune cells that have been selected, expanded or genetically modified to recognise malignant cells. Chimeric antigen receptor T-cell therapy is a prominent example in which a patient's T cells are engineered to express receptors that recognise a specified antigen and then expanded before being returned to the patient. This approach has produced important responses in selected blood cancers. Other cellular approaches include tumour-infiltrating lymphocyte strategies and investigational engineered immune-cell platforms.
The effectiveness of cellular therapies depends on the presence and accessibility of suitable tumour-associated targets and on the ability of transferred cells to survive, expand and function within the patient's body. Some therapies can cause substantial inflammatory or immune complications, including cytokine release syndrome and neurological toxicity in relevant cellular-treatment settings. Manufacturing is also complex because cells may need to be collected, transported, modified, expanded and tested before administration. Cellular Immunotherapy therefore represents a highly specialised intersection of oncology, immunology, genetics, cell manufacturing and clinical medicine rather than simply another category of conventional drug therapy.
Monoclonal antibodies can function as Immunotherapy through several mechanisms. Some antibodies bind directly to molecules on cancer cells and can mark them for immune destruction, recruit immune effector cells or interfere with growth signals. Other antibodies alter immune regulation rather than binding primarily to the malignant cell. Antibody-dependent cellular cytotoxicity and complement activation are examples of immune mechanisms that can contribute to anti-cancer effects.
Some antibody therapies are conjugated to toxins or radioactive substances, combining targeted recognition with delivery of another cytotoxic mechanism; these approaches are related to targeted treatment and immunological recognition but are mechanistically distinct from checkpoint inhibition. Cancer vaccines represent another immunotherapeutic concept, aiming to stimulate an immune response against tumour-associated or tumour-specific antigens.
Preventive vaccines against cancer-causing infections, such as HPV and hepatitis B vaccination, are different from therapeutic cancer vaccines because they prevent infection-associated cancers rather than treating an established malignancy. Distinguishing these uses is important because the word vaccine can refer to prevention or to experimental or established therapeutic strategies depending on context.
The tumour microenvironment strongly influences Immunotherapy. Tumours can contain immune cells, stromal cells, abnormal blood vessels and signalling molecules that either support or inhibit immune activity. Some tumours are relatively inflamed and contain T cells capable of recognising malignant cells, whereas others have few effective immune cells within the tumour. Cancer cells can alter antigen presentation, secrete immunosuppressive factors and recruit cell populations that reduce immune activity. Physical barriers and abnormal vasculature can also limit immune-cell access.
These differences contribute to the variable effectiveness of immunotherapy among tumour types and individuals. A tumour may also evolve under immune pressure by losing the antigen recognised by immune cells or altering pathways required for immune recognition. Combination treatment can attempt to overcome several mechanisms simultaneously, but greater immune activation can increase toxicity. Research therefore seeks biomarkers that characterise the immune environment and identify which patients are most likely to benefit from particular immunotherapeutic strategies.
Immune-related adverse effects are an important distinction between Immunotherapy and many other cancer treatments. Because checkpoint inhibitors and related treatments can increase immune activity, the immune system may attack normal organs and produce inflammatory conditions. Effects can involve the skin, bowel, liver, lungs, endocrine glands, kidneys, nervous system, heart or other tissues. Some are mild and manageable, while others can be severe or potentially life-threatening if not recognised promptly.
Endocrine effects can sometimes result in long-lasting hormone deficiencies even after immunotherapy has stopped. Management often involves withholding treatment and using immune-suppressing medicines such as corticosteroids when clinically indicated, with the exact approach depending on the affected organ and severity. Importantly, not every symptom occurring during immunotherapy is immune-mediated; infection, cancer progression and unrelated conditions remain possible explanations. Diagnosis of treatment toxicity therefore requires clinical assessment rather than assuming that every new symptom is caused by the therapy. Monitoring and rapid recognition are integral components of safe immunotherapy delivery.
Response patterns with Immunotherapy can differ from those of conventional cytotoxic treatment. Some patients experience rapid tumour reduction, while others may have delayed responses. In selected circumstances, inflammatory immune-cell infiltration can temporarily enlarge lesions or make them appear more prominent on imaging, creating a phenomenon historically described as pseudoprogression. This does not mean that every apparent increase in tumour size during immunotherapy represents immune activation; genuine progression remains common and requires careful assessment.
Response criteria have therefore been adapted for some immunotherapy trials and clinical contexts. Durable responses can occur in a subset of patients, sometimes lasting long after treatment has ended, which is one of the distinctive features of successful immune-based treatment. However, durable benefit is not universal, and resistance can arise through loss of tumour antigens, altered antigen presentation, changes in interferon signalling, immune exclusion and other mechanisms. Treatment may consequently involve sequential or combination approaches designed to overcome primary or acquired resistance.
The development of Immunotherapy reflects advances in understanding immune recognition, tumour antigens and inhibitory immune signalling. Earlier attempts to stimulate immunity against cancer produced inconsistent results, but advances in molecular immunology identified mechanisms by which tumours suppress T-cell responses. The clinical development of checkpoint inhibitors demonstrated that releasing specific inhibitory pathways could produce substantial and sometimes durable responses in multiple cancers. Subsequent progress in cellular engineering expanded the potential of immune-based treatment, particularly for selected blood malignancies.
Immunotherapy has also changed the concept of treatment response by showing that effective cancer control can sometimes arise from sustained immune activity rather than continuous direct exposure to a cytotoxic drug. Its limitations include variable response rates, immune-related toxicity, complex manufacturing for some cellular treatments, high treatment costs in some healthcare systems and the difficulty of predicting benefit for individual patients. Future development focuses on improving biomarkers, engineering more effective immune cells, combining immunotherapy with other modalities and overcoming mechanisms that allow tumours to evade immune recognition.
