What Does Antibody-Drug Conjugate Mean?

An antibody-drug conjugate, usually shortened to ADC, is one molecule built from three pieces.

The antibody is the aiming system. It is designed to stick to a specific protein found on the surface of certain cancer cells.

The payload is a cell-killing drug, generally too toxic to give on its own at that strength.

The linker joins them. It has to hold on in the bloodstream. Then it must let go once the package is pulled inside the target cell.

The cell binds the antibody, swallows it, and the payload is released inside. That is the design. It is chemotherapy with an address label, not a gentler drug.

NIH's LiverTox database records the target, the payload, the approval year, and the dose for each.

Trastuzumab deruxtecan. The antibody targets HER2, the human epidermal growth factor receptor 2. The payload, deruxtecan, blocks topoisomerase I. That is an enzyme cells need to untangle DNA. It was approved in 2019. It is used in HER2-expressing breast, gastric, and lung cancers that carry HER2, after earlier treatment. It is given by vein every three weeks, at a weight-based amount that differs between breast and lung cancer.

Brentuximab vedotin. The antibody targets CD30, a marker on certain lymphoma cells. The payload is monomethyl auristatin E, shortened to MMAE. It wrecks microtubules, the scaffolding a cell needs to divide. It was approved in 2011. It treats Hodgkin lymphoma and anaplastic large cell lymphoma that came back or did not respond. It is given by vein every three weeks, at a weight-based amount that is reduced when the liver is not working well.

Sacituzumab govitecan. The antibody targets Trop-2, a protein on the surface of many solid tumors. The payload, govitecan, is another topoisomerase I inhibitor. It was approved in 2020 for triple-negative breast cancer. Urothelial cancer followed in 2021, and hormone receptor-positive breast cancer in 2023. It is given by vein on days 1 and 8 of each 21-day cycle, at an amount based on body weight.

Enfortumab vedotin. The antibody targets Nectin-4, an adhesion molecule on urothelial carcinoma cells. The payload is again MMAE. It won accelerated approval in 2019 for advanced urothelial cancer. It was later approved with pembrolizumab for patients who cannot get cisplatin. It is dosed by body weight, up to a ceiling. It is given on days 1, 8, and 15 of a 28-day cycle, or days 1 and 8 of a 21-day cycle.

Notice the pattern above. The payloads sort into two groups, and the group predicts what you will feel.

Microtubule inhibitors, meaning the vedotin drugs, tend to cause peripheral neuropathy. That is numbness, tingling, or weakness starting in the fingers and toes. LiverTox lists it among the common effects of both brentuximab vedotin and enfortumab vedotin.

Topoisomerase I inhibitors, meaning deruxtecan and govitecan, tend to hit the gut and the bone marrow. Diarrhea, nausea, and low blood counts dominate their side effect lists.

This is why "targeted therapy" can be misleading. The aiming is targeted. The payload still acts like the chemotherapy drug it is. Some healthy cells carry the target protein too, and some payload leaks out.

• Interstitial lung disease. LiverTox lists it as a serious risk for trastuzumab deruxtecan. It lists pneumonia and interstitial lung disease for enfortumab vedotin. Lung symptoms on these drugs are never routine.
• Severe neutropenia and severe diarrhea. Both are flagged as life-threatening concerns with sacituzumab govitecan. That is why blood counts are drawn before each dose.
• Progressive multifocal leukoencephalopathy, a rare brain infection, plus severe skin reactions, are listed for brentuximab vedotin.
• Heart effects. Trastuzumab deruxtecan carries a risk of heart failure. It can also cause QTc prolongation, a change in the heart's electrical timing. Expect a heart scan before and during treatment.
• Embryo-fetal toxicity appears across the class, so contraception planning is part of starting any of them.

• Call 911 or go to an emergency department for struggling to breathe, chest pain, confusion, a rigid or severely painful abdomen, or bleeding you cannot stop. Those do not belong on a phone list.
• Fever of 100.4 degrees F, or 38 degrees C, or higher. NCI treats this as urgent during cancer treatment. Counts are often low after these drugs, so treat it as an emergency rather than a message to leave: use the 24-hour number, and go in if nobody answers. Do not take a fever reducer before calling; it can hide the problem.
• Diarrhea. NCI grades up to six bowel movements above your normal daily number as usually manageable at home. Seven or more above your normal is grade 3 or 4, which NCI describes as potentially life-threatening. Count, do not estimate.
• New or worsening cough, breathlessness, or chest tightness. These are the interstitial lung disease symptoms. Report them the day they start.
• Numbness or tingling that spreads past the fingertips or toes, or that makes buttons and stairs hard. Neuropathy is managed by dose changes, and those work better early.
• A rash that blisters, peels, or involves the mouth or eyes.

Seeing "antibody-drug conjugate" in a note does not identify which drug, which line of treatment, or whether you are eligible. Eligibility runs through the target protein. An ADC aimed at HER2 needs HER2 testing on your tumor. One aimed at CD30 needs CD30 on the lymphoma cells.

It also does not tell you the schedule. Compare the four above: every three weeks, versus days 1 and 8 of 21, versus days 1, 8, and 15 of 28. Those make very different demands on your calendar, your rides, and your time off work.

• Which ADC, and what protein does its antibody target?
• Was my tumor tested for that protein, and what was the result?
• Is the payload a microtubule inhibitor or a topoisomerase inhibitor?
• How is my dose worked out, and which days of the cycle do I come in?
• What baseline tests happen first, such as an echocardiogram or lung imaging?
• What symptom means I stop the next dose rather than push through?

For related reading, see Targeted Therapy vs Chemotherapy, Biomarker Testing and Precision Medicine, and Antibody-Drug Conjugates by Cancer Type.

• LiverTox (NCBI Bookshelf, NIH) — Trastuzumab Deruxtecan
• LiverTox (NCBI Bookshelf, NIH) — Brentuximab Vedotin
• LiverTox (NCBI Bookshelf, NIH) — Sacituzumab Govitecan
• LiverTox (NCBI Bookshelf, NIH) — Enfortumab Vedotin
• National Cancer Institute — Diarrhea and Cancer Treatment
• National Cancer Institute — Infection and Neutropenia during Cancer Treatment