Anti-HER2 therapies are targeted agents directed against the human epidermal growth factor receptor 2 (HER2/ERBB2), a receptor tyrosine kinase.
- HER2 is overexpressed or amplified in ~15–20% of breast cancers and some gastric/gastroesophageal cancers.
- HER2 overexpression is associated with aggressive disease and poor prognosis without therapy.
- Anti-HER2 therapies block HER2 signaling, inhibit tumor growth, and improve survival.
Pharmacological Classes & Examples
| Class | Agents | Mechanism | Key Notes |
|---|---|---|---|
| Monoclonal antibodies (mAbs) | Trastuzumab, Pertuzumab, Margetuximab | Bind extracellular HER2 → inhibit dimerization, downstream signaling, and mediate ADCC (antibody-dependent cell-mediated cytotoxicity) | Backbone of HER2 therapy; trastuzumab is standard |
| Antibody–drug conjugates (ADCs) | Ado-trastuzumab emtansine (T-DM1), Trastuzumab deruxtecan (T-DXd) | HER2 antibody linked to cytotoxic drug → delivers chemotherapy directly to HER2+ cells | Higher efficacy in resistant disease, risk of interstitial lung disease with T-DXd |
| Tyrosine kinase inhibitors (TKIs) | Lapatinib, Neratinib, Tucatinib | Oral small molecules that inhibit intracellular HER2 kinase activity (some also block EGFR/HER1) | Useful in CNS disease (tucatinib especially); diarrhea common (neratinib, lapatinib) |
Indications
- Breast cancer (early-stage and metastatic) – HER2-positive disease.
- Gastric / Gastroesophageal junction (GEJ) adenocarcinoma – trastuzumab first-line in HER2+ disease.
- Ongoing studies in other solid tumors (e.g., colorectal, NSCLC with HER2 amplification or mutation).
Key Toxicities & Monitoring (Pharmacist-Relevant)
| Agent/Class | Toxicity | Monitoring |
|---|---|---|
| Trastuzumab, Pertuzumab | Cardiotoxicity (↓LVEF, HF) | Baseline and q3mo echocardiogram or MUGA |
| T-DM1 (Ado-trastuzumab emtansine) | Hepatotoxicity, thrombocytopenia, neuropathy | LFTs, CBC, monitor for bleeding |
| T-DXd (Trastuzumab deruxtecan) | Interstitial lung disease (ILD/pneumonitis), myelosuppression | Monitor respiratory symptoms, CBC |
| TKIs (Lapatinib, Neratinib, Tucatinib) | Diarrhea, hepatotoxicity, hand-foot syndrome | LFTs, manage diarrhea aggressively |
| All | Infusion-related reactions, hypersensitivity | Premedication if needed, monitor during infusion |
Pharmacist Role
- Ensure HER2 status confirmed by IHC (3+) or FISH amplification before therapy.
- Monitor for cardiotoxicity (especially with trastuzumab-based regimens).
- Educate on oral TKIs adherence and diarrhea management.
- Watch for drug interactions (CYP3A4 substrates: lapatinib, neratinib, tucatinib).
- Support combination regimens: anti-HER2 therapy often combined with chemotherapy (docetaxel, paclitaxel, capecitabine) or endocrine therapy in HR+/HER2+ disease.