Monoclonal antibodies

What it is

Monoclonal antibodies are lab-made proteins that bind one specific target, and many cancer treatments use them by IV infusion. The key idea is that each monoclonal antibody is designed to recognise a single antigen or epitope, which helps it act more selectively than many older cancer drugs. In cancer care, monoclonal antibodies may block growth signals, recruit the immune system, carry chemotherapy or radiation to tumour cells, or release immune brakes. The first widely used cancer monoclonal antibody, rituximab, entered clinical use in the late 1990s and helped establish this drug class as a major part of oncology.

Monoclonal antibodies are not one medicine but a broad drug class. Some are used alone, while others are combined with chemotherapy, hormone therapy, targeted therapy, or immunotherapy. They are used in blood cancers and many solid tumours, including breast, colorectal, lung, head and neck, and some gastrointestinal cancers. In India, access depends on the exact drug, indication, biomarker status, hospital protocols, and cost; biosimilars are available for some antibodies and can improve affordability when approved for the same use.

A simple way to think about them is that they are precision proteins. They circulate in the bloodstream, attach to a chosen target, and then trigger a therapeutic effect.

Type of monoclonal antibody approach	What it does	Example use
Naked antibody	Binds a target directly	Rituximab, trastuzumab
Immune checkpoint antibody	Removes immune inhibition	Pembrolizumab, nivolumab
Antibody-drug conjugate	Delivers a toxic payload to target cells	Trastuzumab deruxtecan
Bispecific antibody	Binds two targets at once	Some blood cancer therapies
Radioimmunotherapy antibody	Delivers radiation to target cells	Selected lymphoma settings

How it works

Monoclonal antibodies are made to recognise a specific molecule on a cell or in the circulation. In cancer, that target may be a receptor on tumour cells, a growth factor, or an immune checkpoint such as PD-1 or PD-L1.

Their effects vary by product:

1. Blocking signals: Some antibodies stop cancer cells from receiving growth or survival signals. Trastuzumab, for example, targets HER2-positive cancers.
2. Flagging cells for immune attack: After binding to a cancer cell, the antibody can help immune cells identify and destroy it.
3. Direct cell killing: Some antibodies trigger cell death pathways after attaching to the target.
4. Delivering treatment: Antibody-drug conjugates carry chemotherapy-like payloads, and some antibodies can carry radioactive material.
5. Releasing immune brakes: Checkpoint inhibitors are monoclonal antibodies that help T cells attack cancer more effectively.

Not all monoclonal antibodies work the same way, and not all patients benefit equally. Their usefulness often depends on whether the tumour actually expresses the target. That is why biomarker testing is often needed before treatment. Common examples include HER2 testing in breast or gastric cancer, and PD-L1 or other molecular tests in some lung and other cancers.

Evidence and uses

Evidence for monoclonal antibodies is strong in many cancers, but benefit depends on the exact drug and disease setting. Some are part of standard first-line treatment, while others are used only after earlier treatment stops working.

Examples of established oncology uses include:

• CD20-targeting antibodies for B-cell lymphomas and some leukaemias.
• HER2-targeting antibodies for HER2-positive breast and gastric cancers.
• EGFR-targeting antibodies for selected colorectal and head and neck cancers.
• VEGF-targeting antibodies to reduce tumour blood vessel formation in several cancers.
• Checkpoint inhibitor antibodies in melanoma, lung cancer, kidney cancer, head and neck cancer, and others.

Monoclonal antibodies are also used outside cancer, including autoimmune and inflammatory diseases, but in oncology the main point is that they are targeted biologic drugs rather than traditional small-molecule medicines.

Response can range from dramatic and durable to minimal or absent. Reasons include low target expression, tumour resistance, immune escape, and differences in prior treatment. Some antibodies improve survival, some mainly improve response rates or delay progression, and some are useful only in biomarker-defined groups. For patients and families, this means the name of the antibody alone is not enough; the cancer type, stage, biomarker result, and treatment goal matter.

Safety and interactions

Monoclonal antibodies can cause side effects, and some can be serious. The pattern depends on the specific drug.

Common or important risks include:

• Infusion reactions: fever, chills, rash, breathlessness, low blood pressure, or rarely severe allergic-type reactions, often during or soon after infusion.
• Flu-like symptoms: fatigue, body aches, fever, nausea, or diarrhoea.
• Skin effects: rash is common with some EGFR-targeting antibodies.
• Organ-specific toxicity: some drugs can affect the lungs, liver, bowel, heart, or hormone glands.
• Immune-related adverse events: checkpoint inhibitor antibodies can cause inflammation in almost any organ, including thyroiditis, hepatitis, colitis, pneumonitis, and less commonly myocarditis or neurologic problems.
• Infection risk: some antibodies that affect immune cells can increase susceptibility to infections or reactivate infections.

Some monoclonal antibodies require premedication and close monitoring during infusion. Patients may need blood tests, heart monitoring, or scans depending on the drug. For example, HER2-directed therapy may require heart function assessment because some agents can reduce cardiac function.

Drug interaction issues are usually different from those of tablets metabolised by the liver, but practical interactions still matter. Combining monoclonal antibodies with chemotherapy, steroids, or other immune therapies can increase toxicity. Vaccination timing, infection history, hepatitis B status, and tuberculosis risk may also matter in selected cases. In India, clinicians may screen for infections such as hepatitis B before certain B-cell-depleting therapies.

Do not start, stop, or switch a monoclonal antibody without oncology guidance. If you develop fever, shortness of breath, severe diarrhoea, jaundice, chest pain, confusion, or a rapidly worsening rash during treatment, contact your cancer team urgently.

When to see a clinician

See a clinician if monoclonal antibody therapy has been suggested and you want to understand whether your cancer has the right target, what benefit is realistic, and what monitoring is needed. Ask whether biomarker testing has been done and whether a biosimilar is an option when relevant.

Seek urgent medical care during treatment if you have signs of an infusion reaction, new breathing trouble, severe diarrhoea, dehydration, persistent fever, reduced urine output, chest pain, or sudden weakness. Immune-related side effects can begin during treatment or even after it has stopped, so new symptoms should not be ignored.

Limitations and open questions

Monoclonal antibodies are important drugs, but they are not a cure-all. Many cancers either do not express the target, respond only briefly, or develop resistance over time. Cost, infusion logistics, and access remain major barriers in many settings, including India.

Evidence is strong for many approved uses, but not every antibody helps every patient. Newer formats such as bispecific antibodies and antibody-drug conjugates are expanding options, yet they also bring new safety issues. Research continues on better biomarkers, resistance mechanisms, optimal sequencing with chemotherapy and immunotherapy, and how to make these treatments more accessible.

Another limitation is that broad terms like "monoclonal antibody therapy" can be misleading. The benefits and risks of rituximab, trastuzumab, bevacizumab, cetuximab, and pembrolizumab are very different. The most useful discussion is always about the exact medicine, the exact cancer, and the exact treatment goal.