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Trastuzumab
Source: Breast Cancer Treatment (PDQ®)–Health Professional Version, National Cancer Institute.
Source updated: April 25, 2025 · Captured 2026-09-09.
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Approximately 20% to 25% of patients with breast cancer have tumors that overexpress HER2.[64] Trastuzumab is a humanized monoclonal antibody that binds to the HER2 receptor.[64] In patients previously treated with cytotoxic chemotherapy whose tumors overexpress HER2, administration of trastuzumab as a single agent resulted in a response rate of 21%.[65][Level of evidence C3]
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Evidence (trastuzumab):
In a phase III trial, patients with metastatic disease were randomly assigned to receive either chemotherapy alone (doxorubicin and cyclophosphamide or paclitaxel) or the same chemotherapy plus trastuzumab.[66][Level of evidence A1]
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In a phase III trial, patients with metastatic disease were randomly assigned to receive either chemotherapy alone (doxorubicin and cyclophosphamide or paclitaxel) or the same chemotherapy plus trastuzumab.[66][Level of evidence A1]
Patients treated with chemotherapy plus trastuzumab had an OS advantage over those who received chemotherapy alone (25.1 months vs. 20.3 months, P = .05).[66][Level of evidence A1]
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Notably, when combined with doxorubicin, trastuzumab is associated with significant cardiac toxicity.[67]
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Clinical trials comparing multiagent chemotherapy plus trastuzumab with single-agent chemotherapy have yielded conflicting results.
In one randomized study of patients with metastatic breast cancer treated with trastuzumab, paclitaxel, and carboplatin, patients tolerated the combination well and had a longer time to disease progression, compared with those treated with trastuzumab and paclitaxel alone.[68][Level of evidence B1]
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However, no difference in OS, time to disease progression, or response rate was shown in the Breast Cancer International Research Group’s phase III trial (BCIRG-007 [NCT00047255]) that compared carboplatin and docetaxel plus trastuzumab versus docetaxel plus trastuzumab as first-line chemotherapy for metastatic HER2-overexpressing breast cancer.[69][Level of evidence A1]
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Outside of a clinical trial, standard first-line treatment for metastatic HER2-overexpressing breast cancer is single-agent chemotherapy plus trastuzumab.
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Preserved source evidence · Not medical advice