Antibody-Drug Conjugates — Immunotherapy or Chemotherapy?

No. Not in the way the word is normally used. An antibody-drug conjugate uses an antibody as a delivery vehicle for a chemotherapy drug. The antibody finds the cell. The chemotherapy kills it. Your immune system is not switched on, released or recruited. Guideline bodies classify this class as targeted therapy, not immunotherapy.

The confusion is understandable. Checkpoint inhibitors are antibodies. Bispecific antibodies are antibodies. Antibody-drug conjugates are antibodies too. All three arrive by infusion, all three are described as modern, and all three are spoken about in the same breath. But an antibody is a shape, not a mechanism. What matters is what the antibody is being used for.

• Checkpoint immunotherapy — the antibody blocks a stand-down signal, so immune cells that were already there become active again. The immune system does the treating.
• Bispecific antibodies — the antibody holds an immune cell and a cancer cell together so the immune cell can act. The immune system still does the treating.
• Antibody-drug conjugates — the antibody carries a chemotherapy drug to a cell and delivers it inside. A drug does the treating. The immune system is a bystander.

This is not a semantic point. It is the difference between expecting immune reactions managed with steroids and expecting low blood counts, hair loss and nerve tingling. Getting the label wrong means preparing for the wrong six months.

Every antibody-drug conjugate is built from three parts, and each part fails differently. Knowing which part is which makes the side-effect list further down predictable rather than alarming.

1. 1

   The antibody finds its marker

   The antibody is built to recognise one specific protein sitting on the outside of a cell — HER2 is the marker most patients have heard of, and there are several others tested on tumour tissue. This is why eligibility is decided by a laboratory test on your biopsy or surgical specimen, not by the cancer type alone. No marker, no delivery, no point.

2. 2

   The cell pulls the package inside

   Binding an antibody to a surface receptor makes the cell draw the whole complex in. That is ordinary cell behaviour being used against it. The package now sits inside an internal compartment, cut off from the rest of the body.

3. 3

   The linker lets go

   The linker is the chemical bond holding the drug to the antibody, and it is the most engineered part of the whole design. It has to hold firm for hours in the bloodstream and then release inside the cell, usually triggered by the acidic, enzyme-rich compartment it has been delivered into. Linkers that let go too early are why some payload always reaches healthy tissue.

4. 4

   The payload does the damage

   Two payload families dominate. One disrupts the internal scaffolding a cell needs in order to divide. The other damages DNA or the enzymes that repair it. Both are conventional chemotherapy mechanisms, delivered in an unconventional way. With some designs the released payload can also drift into neighbouring cells, which is useful when not every cancer cell carries the marker.

Nothing in those four steps requires a functioning immune response. That is the whole basis of the classification, and of everything on the rest of this page. Mechanism descriptions here follow NCCN and ESMO patient-education material as of August 2026.

This table separates mechanisms. It does not rank them. These classes are used in different cancers, at different stages, on different evidence, and no comparison of one against another is made or implied here.

• Blood counts move to the centre of the plan — a blood test before each cycle is not administrative. It decides whether the cycle goes ahead, at what dose, or is postponed.
• Infection risk is real and timed — the days after each infusion are when white cells dip. Fever in that window is treated as an emergency, which is not how a fever is handled on checkpoint treatment.
• Steroids are not the default answer — the steroid-managed immune reactions of checkpoint treatment, such as immune colitis or thyroiditis, are not the pattern here. Management follows chemotherapy toxicity protocols instead.
• Late reactions after finishing are less of a concern — checkpoint immunotherapy can produce reactions weeks after the last dose because the immune system stays engaged. Payload effects largely track the drug, with nerve symptoms the main exception, as they can persist.
• Eligibility rests on a marker, not on the diagnosis alone — the laboratory test on your tumour tissue decides this. If the marker is absent or was never tested, the treatment is not appropriate, and asking for that result in writing is reasonable.

Response assessment is by scan on a schedule your team sets. At CION, treatment of this kind is given as day care, and response-assessment PET-CT is coordinated at partner imaging centres rather than performed in-house. Availability of any specific agent in India depends on its Central Drugs Standard Control Organisation approval status and on supply, both of which vary agent by agent — ask your treating team about the exact agent being proposed.

If you were told the word immunotherapy and this page has changed what you thought you were getting, that is worth raising directly with your oncologist. It is a common, honest shorthand rather than a mistake — but you are entitled to the precise class in writing.

• Cytokine Therapy: Interferon, Interleukin and Where They Stand Now — the original immune-stimulating class, and an honest account of where it still has a role.
• Oncolytic Virus Therapy: Using a Virus to Attack Cancer — a genuinely immune-directed approach that sounds stranger than an antibody carrying a drug, and is far less widely available.
• Tumour-Infiltrating Lymphocyte (TIL) Therapy — immune cells taken from the tumour itself, grown and returned. A cell therapy, which CION does not provide; the page is orientation and referral content.
• Immunotherapy at CION Cancer Clinics — the hub page: biomarker testing, day-care administration, monitoring and support in one place.

This page explains a class of treatment from a scientific standpoint. It is general information, not a treatment recommendation, and not a substitute for consultation with your own oncologist. No brand, product or molecule is named or endorsed here, and no comparison of one product against another is made. Immunotherapy is administered as day care at CION centres; response-assessment PET-CT is coordinated at partner imaging centres. CION does not provide CAR-T or cell therapy. Any cost discussed with you is indicative only, as of August 2026. Only your treating team, reviewing your complete case, can say whether any of this applies to you.

Asking what a treatment actually is comes before agreeing to it

Wanting to understand the mechanism before the first infusion is not scepticism — it is how you prepare properly. Our team takes the time to explain the class, the schedule and what to watch for.