Which of the following oncogenes, when activated, primarily functions as a growth factor receptor tyrosine kinase?

Explanation

## Oncogene Classification by Function **Key Point:** Oncogenes are classified based on their cellular function. Growth factor receptor tyrosine kinases (RTKs) are a major class of proto-oncogenes that, when activated, drive proliferation through ligand-independent or ligand-dependent signaling. ### HER2 (ERBB2) — Growth Factor Receptor HER2 is a transmembrane receptor tyrosine kinase belonging to the EGFR family. When overexpressed or mutated: - Constitutively active or hypersensitive to growth factors - Drives proliferation in ~20% of breast cancers - Targetable by trastuzumab (Herceptin) ### Comparison of Oncogene Types | Oncogene | Class | Function | Example Cancer | | --- | --- | --- | --- | | HER2 | Growth factor receptor | RTK signaling | Breast cancer | | MYC | Transcription factor | Gene transcription | Burkitt lymphoma | | RAS | Signal transduction | GTPase/relay protein | Pancreatic cancer | | TP53 | Tumor suppressor (not oncogene) | Cell cycle checkpoint | Li-Fraumeni syndrome | **High-Yield:** HER2 and EGFR are the prototypical RTK oncogenes tested in NEET PG. Remember: RTKs have extracellular ligand-binding domains and intracellular kinase domains. **Clinical Pearl:** HER2 testing (IHC or FISH) is mandatory in breast cancer diagnosis because HER2-positive tumors have different prognosis and respond to targeted therapy.