Monoclonal Antibodies: Drugs That Bind to a Single Target

What is it?

A monoclonal antibody is a drug produced to mimic the antibodies of the immune system and to bind to a single target protein. The word monoclonal in its name means that it is multiplied from a single cell clone.

In oncology, some antibodies cut the growth signal of the tumour, some affect blood-vessel formation and some lift the brake on the immune system. All are antibodies in form, but their tasks are not the same. For this reason the drug name and the target protein are written separately on the report.

How does it work?

Trastuzumab and pertuzumab bind to the HER2 protein, rituximab to the CD20 protein, cetuximab to the EGFR protein, and bevacizumab to vascular endothelial growth factor. Binding can cut the cell’s signal or make it easier for immune cells to recognise the tumour.

Pembrolizumab and nivolumab are also monoclonal antibodies; their mode of action is described on the immunotherapy page. Loading chemotherapy onto the tip of an antibody is the subject of the antibody-drug conjugate page.

In which cancers is it used?

Examples include trastuzumab in HER2-positive breast and some stomach cancers, rituximab in some B-cell lymphomas, cetuximab in selected patients with colorectal cancer, and regimens containing bevacizumab in many tumours.

Which treatment is appropriate is discussed at the tumour board, with the relevant specialties taking part, by considering the type, stage and molecular features of the cancer and the person’s general condition together. For most antibodies, whether the target is present in the tumour is tested before treatment.

How is it given?

The drug is usually given as an infusion in a day-treatment unit. The first administrations are given more slowly; blood pressure, temperature and breathing are monitored during the infusion. The interval can be two or three weeks and can be timed on the same day as chemotherapy.

With some drugs such as trastuzumab, heart function is checked by echocardiography at set intervals. With vessel-targeted drugs such as bevacizumab, dental care and wound healing are planned around the surgery schedule.

During follow-up, blood tests, imaging and symptom review are read together. The dose or date may be changed according to side effects and organ function. The list of medicines used at home is updated at every visit. Sudden fever, shortness of breath, uncontrolled diarrhoea or bleeding should be reported the same day.

Possible side effects

Chills, fever, rash or a fall in blood pressure may occur during the infusion. In the following days fatigue, diarrhoea or delayed wound healing may be seen. Trastuzumab is more concerned with the heart muscle, bevacizumab with blood pressure and bleeding, and cetuximab with skin rash.

The symptom is most often manageable. With severe allergy, chest pain or shortness of breath, the administration is stopped and an emergency assessment is made.