Herceptin (Trastuzumab): What It Is and What to Expect

HER2 is a receptor on the surface of cells. Some cancers carry far too much of it. That surplus tells the cell to keep growing.

NCI describes the drug in two steps. It binds to HER2 and blocks it. It then sets off an immune reaction that kills cells carrying a lot of HER2.

It is a monoclonal antibody. That means a lab-made protein built to stick to one target.

So the test matters more here than the diagnosis. A breast cancer without extra HER2 gets nothing from this drug.

The label is unusually prescriptive about testing.

Patients are picked on one of two findings. Extra HER2 protein on the cells. Or extra copies of the HER2 gene. The tests must be FDA-authorized. The lab must have shown it can run them well.

Gastric cancer gets its own rule. In stomach tumors the staining is often incomplete around the cell edge. It is patchier than in breast tissue. So the label calls for a test made for gastric cancer. It also warns that badly fixed tissue can give unreliable results. So can the wrong reagents, or missing controls.

• Adjuvant breast cancer. HER2-overexpressing disease, with or without node involvement. It is given inside a regimen of doxorubicin and cyclophosphamide, plus paclitaxel or docetaxel. Or with docetaxel and carboplatin. Or on its own, after anthracycline-based therapy.
• Metastatic breast cancer. With paclitaxel as first-line treatment. Or alone after one or more chemotherapy regimens for metastatic disease.
• Metastatic gastric cancer. With cisplatin, plus either capecitabine or fluorouracil. The tumor must be HER2-overexpressing. It must sit in the stomach or at the gastroesophageal junction. And it must not have been treated before for metastatic disease.

Trastuzumab is given into a vein only. The label says not to give it as an intravenous push or bolus.

• Adjuvant breast, weekly start. A larger first infusion over 90 minutes, then smaller weekly infusions over 30 minutes. Twelve weeks with paclitaxel or docetaxel. Eighteen weeks with docetaxel and carboplatin. One week after the last weekly dose, it changes to a three-weekly schedule. Total time on treatment is 52 weeks.
• Adjuvant breast, three-weekly. A larger first infusion over 90 minutes, then a smaller one over 30 to 90 minutes every 3 weeks, for 52 weeks.
• Metastatic breast. A larger first infusion over 90 minutes, then smaller weekly ones over 30 minutes.
• Metastatic gastric. A larger first infusion over 90 minutes, then a smaller one over 30 to 90 minutes every 3 weeks.

The first infusion is longer than the rest on every schedule. That is deliberate, and it is about infusion reactions rather than the dose.

A boxed warning is the strongest warning the FDA can require. Trastuzumab has one, covering four things.

Cardiomyopathy. The drug can cause heart failure. Early on it may cause no symptoms at all. The pumping fraction falls. Risk is highest when anthracyclines are given at the same time. So ejection fraction is measured in everyone before treatment. It is measured again at intervals during it. In adjuvant treatment, a clear fall means stopping. In metastatic disease it means holding.

Infusion reactions and lung toxicity. Serious reactions can occur, and some are fatal. They usually start during the infusion, or within 24 hours. The infusion is paused for breathlessness. It is paused for a marked drop in blood pressure. It is stopped for good after anaphylaxis, angioedema, interstitial pneumonitis, or acute respiratory distress syndrome.

Embryo-fetal toxicity. Exposure in pregnancy can cause oligohydramnios. That means too little amniotic fluid. It has led to underdeveloped lungs, skeletal problems and newborn death. Pregnancy status is checked before treatment starts. Effective contraception is advised.

Several drugs share part of this name and are not interchangeable.

NCI lists seven US brand names for trastuzumab itself. Herceptin. Hercessi. Herzuma. Kanjinti. Ogivri. Ontruzant. Trazimera. Those are versions of the same molecule.

Then come the ones that are genuinely different drugs. The label states it plainly. Do not swap Herceptin for ado-trastuzumab emtansine. Do not swap it for fam-trastuzumab deruxtecan. Dosing also differs from the under-the-skin trastuzumab products. NCI lists two of those separately. One is trastuzumab and hyaluronidase-oysk. The other combines pertuzumab, trastuzumab and hyaluronidase-zzxf. Each has its own summary.

Checking which product is being given is a reasonable thing to do out loud.

• Which HER2 test was run, and what did it show?
• Was the assay the right one for this cancer site?
• Which product is being given, and does the label on the bag match the plan?
• Has an ejection fraction been recorded, and what was the number?
• Is an anthracycline part of this regimen?
• How long will the first infusion take, and who watches during it?
• What happens if a chill or a fever starts on the chair?
• Is contraception needed, and for how long after the last dose?

A year of treatment is a long commitment. Most of what makes it go smoothly is set up before the first bag is hung: the right test, a baseline heart measurement, and the correct product name written on the order.

This page is a summary and does not replace the prescribing information.

The FDA-approved label is on DailyMed. The approval history sits under Biologic License Application 103792 in Drugs@FDA. Both carry the current Boxed Warning. Both carry the Warnings and Precautions, and the patient leaflet.

Trouble breathing, chest pain, confusion, heavy bleeding or swelling of the face, lips or throat are emergencies whatever the drug: call 911. A fever during chemotherapy is also urgent — ring the care team's 24-hour number straight away, and do not wait for office hours.

For where this fits in a plan, see targeted therapy and understanding your treatment plan.

• NCI — Trastuzumab
• openFDA drug label API — Herceptin (trastuzumab), BLA103792
• Drugs@FDA — BLA 103792 (HERCEPTIN, Genentech)
• DailyMed — trastuzumab label search