Trastuzumab

Trastuzumab is a humanized monoclonal antibody used to treat cancers that overexpress the HER2 receptor (ERBB2). It binds to the extracellular domain of HER2 on tumor cells, blocking signaling and mediating antibody-dependent cellular cytotoxicity, which can slow or stop tumor growth.

In breast cancer, trastuzumab is indicated for HER2-positive disease in several settings, including metastatic disease and early-stage cancer as adjuvant or neoadjuvant therapy. In gastric or gastroesophageal junction cancer, it is used in combination with chemotherapy for HER2-positive tumors. Regimens often pair trastuzumab with taxanes or platinum-based chemotherapy, with treatment duration guided by response and tolerability.

Dosing and monitoring: trastuzumab is given by intravenous infusion. Regimens vary; typical metastatic regimens start with a loading dose of 8 mg/kg, followed by 6 mg/kg every 3 weeks. Adjuvant therapy commonly uses a similar schedule for up to one year. Cardiac function should be monitored with echocardiography or MUGA scans before and during treatment due to the risk of cardiomyopathy, especially when used with anthracyclines.

Adverse effects include infusion reactions, fever, chills, rash, nausea, diarrhea, and anemia. Serious risks include cardiomyopathy and fetal harm; pregnancy should be avoided unless clearly needed, and fetal testing may be warranted. The combination with anthracyclines increases the risk of cardiac toxicity; caution is advised when coadministering these agents.

Discovery and availability: trastuzumab was developed by Genentech and approved in 1998 for metastatic breast cancer, establishing HER2-targeted therapy as a standard approach. Multiple biosimilars have been approved in various regions, expanding access to the therapy.