Which of the following drug acts by inhibiting tyrosine kinase activated by EGF receptor as well as HER2 ?
**Core Concept**
The question is testing the student's knowledge of targeted cancer therapy, specifically tyrosine kinase inhibitors (TKIs) that target the epidermal growth factor receptor (EGFR) and human epidermal growth factor receptor 2 (HER2) pathways.
**Why the Correct Answer is Right**
Trastuzumab is a monoclonal antibody that binds to the extracellular domain of the HER2 receptor, preventing its dimerization and subsequent activation of tyrosine kinase. This inhibits the signaling pathway that leads to cell proliferation and survival. Additionally, it has been shown that trastuzumab can also inhibit the phosphorylation of EGFR, further inhibiting the tyrosine kinase pathway.
**Why Each Wrong Option is Incorrect**
* **Option A:** Lapatinib is a dual TKI that targets EGFR and HER2, but it does not inhibit the EGF receptor directly.
* **Option B:** Gefitinib is a TKI that specifically targets the EGFR tyrosine kinase, but it does not have activity against HER2.
* **Option D:** Erlotinib is another EGFR TKI, but it does not have activity against HER2.
**Clinical Pearl / High-Yield Fact**
Trastuzumab is a key component of the treatment regimen for HER2-positive breast cancer, and its use has significantly improved outcomes for patients with this subtype of cancer.
**Correct Answer:** D. Trastuzumab.