Share
Antibody, linker and payload
An antibody-drug conjugate, or ADC, combines an antibody, a connecting linker and a cell-killing medicine called the cytotoxic payload (often a potent chemotherapy drug). The antibody recognises a particular molecule called an antigen. Every ADC has a biological target, although not every approved use requires a separate companion diagnostic: a test used to help determine whether a particular medicine is suitable.
How an ADC can act
After binding its target, an ADC is commonly taken into a cell and processed so that the payload can act. The details differ between medicines. Some payloads can also affect nearby cells, called a bystander effect; this is not a feature of every ADC.
How treatment types compare
| Feature | Standard chemotherapy | Targeted therapy | ADC |
|---|---|---|---|
| Main concept | Interferes with cancer-cell growth or division | Acts on a relevant molecular feature or pathway | Antibody links target recognition to cytotoxic delivery |
| Selection | Cancer type, setting and fitness | Disease setting and relevant biology | Exact drug indication, disease setting and any required target test |
| Target or test | Usually no drug-specific antigen test | Testing often guides selection; requirements vary | Always a target; separate testing is indication-dependent |
| Delivery | Often intravenous or oral | Oral or intravenous | Usually intravenous |
| Side effects | Healthy tissues can be affected | Drug and pathway-specific effects | Payload, antibody and drug-specific effects |
Choosing an ADC
Selection depends on the tumour type, treatment history, any required biomarker result and evidence for the exact medicine and combination. A biomarker is a measurable feature of the cancer, such as a protein or genetic change. Availability and individual suitability should be discussed with the treating team. An approval or guideline recommendation for one cancer or treatment setting does not automatically apply to another.
Where ADCs fit into a treatment plan
ADCs bring together target recognition and delivery of a potent anticancer payload. They are used in selected solid cancers and blood cancers. Their role may be after another treatment, in a combination or in an earlier treatment setting, depending on the exact medicine and evidence. The group is developing rapidly, so a treatment mentioned in the news may not match your diagnosis or local access.
ADCs are not all interchangeable. Two drugs aimed at the same target can carry different cytotoxic payloads, behave differently and have different side effects. Your oncologist should explain why a particular ADC is being considered, its expected benefit and the alternatives in your situation.
Understanding the target and any required test
The target is often a protein on the cell surface. For some treatments, the amount or pattern of that protein helps determine eligibility; other indications do not require a separate target test. The required test and threshold depend on the actual drug and cancer setting. A broad sequencing report may not provide the protein information needed.
An older sample can sometimes be used, while a review or another sample may be appropriate if the disease has changed or the result is unclear. Ask whether the proposed test is necessary for this treatment and how it will affect the recommendation. The presence of a target supports selection in the right context but does not guarantee a response.
Planning your venous access
ADCs are generally given through a drip into a vein (intravenous infusion). Your team selects a suitable way to reach the vein, called venous access, for the specific medicine and schedule. Report pain, burning or swelling immediately, even if you have a port.
Ports, PICCs, and venous accessPreparing for an ADC infusion
ADCs are usually given into a vein on a repeating schedule. Before treatment, the team checks symptoms, blood counts and organ function, with extra assessments for particular medicines. Anti-sickness medicines or other premedication may be prescribed. The first infusion can involve additional observation.
Tell the team about existing lung problems, numbness, eye symptoms and heart disease. Report any new problem before the next cycle rather than waiting until the infusion has started. Ask whether a cannula (a small tube in a vein), a peripherally inserted central catheter (PICC, a longer line placed through an arm vein), or a port under the skin best suits the complete plan, especially if other infused drugs are included.
Monitoring and side effects
Different ADCs have different risks. These can include low blood counts, nausea, nerve problems, lung inflammation, skin effects or eye problems, depending on the medicine. Allergic reactions, including anaphylaxis, can also occur. Ask which symptoms need immediate action and which tests or eye assessments are required.
Why the exact drug matters for side effects
An ADC can still affect healthy tissues. Effects may come from the payload, target and other features of the medicine. Low blood counts, fatigue, nausea, bowel changes and hair loss occur with some ADCs, while particular drugs may require closer attention to nerves, lungs, skin, eyes, liver or heart function. These are not equally likely with every ADC.
Ask for the name of the medicine and its specific symptom and monitoring plan. If eye assessments or prescribed preventive eye care are required, keep them on schedule even when vision feels normal. New tingling or numbness should also be reported early because it can affect later treatment decisions.
Symptoms that need prompt attention
Contact the team promptly for a new cough or breathlessness, a new visual problem, persistent diarrhoea, significant rash or worsening numbness. Some ADCs can cause lung inflammation, so a breathing symptom should not simply be put down to a cold. The team will assess other causes as well, including infection.
Fever of 38°C (100.4°F) or higher, shaking chills or sudden illness needs immediate advice and prompt assessment, particularly when blood counts may be low. Follow a lower temperature threshold if your unit has given one. Severe breathing difficulty, chest pain, collapse, confusion or uncontrolled bleeding needs emergency care. Do not wait for a routine message reply.
Assessing benefit and adjusting the plan
The team assesses benefit using the appropriate symptoms, examination and scans. Side effects alone do not show whether treatment is working. A treatment pause or dose reduction may be needed to manage toxicity; certain problems require stopping a particular drug.
If the cancer progresses, the next decision considers previous treatments, remaining options and your priorities. Changing from one ADC to another is not automatically helpful, even when their names or targets differ. Supportive care, rehabilitation and nutrition remain important alongside whichever treatment is chosen.
Questions for your oncologist
- Which target does this medicine recognise?
- Does my indication require a specific biomarker result?
- What benefit is expected in my treatment setting?
- Which symptoms should I report urgently?
- What alternatives are appropriate?
Frequently asked questions
Is an ADC chemotherapy or targeted therapy?
It combines aspects of both: an antibody recognises a target and carries a cytotoxic payload. This helps explain both its potential benefit and its side effects. It should not be described as chemotherapy with no effect on healthy cells.
Is an ADC the same as a monoclonal antibody?
An ADC includes an antibody linked to a payload. A monoclonal antibody without that payload is a different product, even if part of its name is similar. Always use the complete medicine name when discussing treatment.
Is an ADC the same as immunotherapy?
It is not the same as checkpoint-inhibitor immunotherapy. ADCs mainly use an antibody to deliver a payload. Some treatment regimens combine an ADC with immunotherapy, and then both sets of precautions need to be understood.
Do all ADCs need a biomarker test?
Every ADC recognises a target, but a separate eligibility test is not required for every drug indication. When a test is required, the method and result must match the particular medicine and cancer setting.
Does HER2-low mean the same as HER2-positive?
HER2 stands for human epidermal growth factor receptor 2, a protein involved in cell growth. HER2-low and HER2-positive are distinct test descriptions, and their treatment implications depend on the cancer and drug. Certain ADCs have evidence in specific lower-expression settings, but this does not make every HER2-directed treatment suitable. Ask the team to interpret your pathology report.
What is the bystander effect?
With some ADCs, released payload can affect nearby cells as well as the cell that first took up the drug. This is a property of particular medicines, not every ADC, and does not mean the treatment can be used for any cancer.
Is an ADC always safer than standard chemotherapy?
No. The side-effect pattern is different and depends on the exact drug. Some people tolerate a particular ADC well; others need adjustments or a different treatment. Compare likely benefits and risks for the actual options available to you.
Will I lose my hair?
Some ADCs cause hair loss and others are less likely to do so. Ask about the specific medicine and any combination treatment. The amount of hair loss does not indicate how well treatment is working.
Why are lung symptoms taken seriously?
Certain ADCs can cause lung inflammation that needs early assessment. New cough or breathlessness can also have other causes. Contact the team promptly rather than trying to identify the cause yourself.
Why might I need eye checks?
Some ADCs have particular eye-related risks and require an eye-care plan. The instructions differ by drug. Attend scheduled checks and report pain, dryness or visual changes; do not copy another patient’s eye-drop regimen.
What if I already have numb hands or feet?
Tell the oncologist before treatment. Existing neuropathy can affect selection and monitoring. Report any worsening, especially if it affects walking, balance, buttons or other daily tasks.
Can an ADC be combined with another treatment?
Yes, in specific regimens supported by evidence. It is not safe to assume that adding chemotherapy or immunotherapy will help. The combination may change both effectiveness and side effects.
Is a port essential?
Not always. Venous access is selected according to the drug, schedule, vein condition and overall treatment plan. Ask about a cannula, PICC or port before treatment begins.
How many cycles will I receive?
There is no universal number. Some treatment settings use a defined course; others continue while benefit and tolerability justify it. Ask when the first review will happen and what would lead to a pause or change.
Does a dose reduction mean treatment is no longer useful?
Not necessarily. Drug-specific reductions can help manage side effects and permit continued treatment. Your team balances the treatment goal and tolerability; do not alter the dose yourself.
Can another ADC work after one stops working?
Sometimes, but it depends on the cancer, prior drugs, targets, payloads and evidence for the next option. Resistance may overlap. This requires a fresh treatment discussion rather than automatic substitution.
What about pregnancy and breastfeeding?
ADCs may harm a developing baby, and breastfeeding may be unsafe during and for a period after treatment. Ask for the exact precautions for your medicine and discuss fertility before starting.
Which questions should I ask at the consultation?
Ask for the full drug name, why it fits your cancer, whether a target test is required, what benefit is expected and what alternatives exist. Confirm the infusion schedule, supportive medicines, monitoring and urgent contact plan.
Related guides
Sources and further reading
- Macmillan: Antibody Drug Conjugate Treatment
- NCI: Targeted Therapy to Treat Cancer
- NCI: trastuzumab deruxtecan and HER2-low breast cancer — trial background (2022)
- NCI: infection and neutropenia during cancer treatment
- FDA: mirvetuximab soravtansine for FRα-positive, platinum-resistant ovarian, fallopian tube or peritoneal cancer (2024)
