A 63-year-old woman discovers a lump in her right breast. Mammography confirms the presence of a suspicious “lump,” and a needle core biopsy is performed to determine whether the mass is malignant. The pathology repo confirms that the mass is indeed cancerous and that the tissue demonstrates amplification of the Her-2/neu oncogene. The gene product of Her-2/neu is what kind of protein?

**Core Concept**
The Her-2/neu oncogene is a member of the epidermal growth factor receptor (EGFR) family and plays a significant role in the development and progression of breast cancer. The gene product of Her-2/neu is a transmembrane receptor tyrosine kinase that, when overexpressed, contributes to oncogenesis by promoting cell proliferation and survival.

**Why the Correct Answer is Right**
The Her-2/neu gene product is a 185-kDa transmembrane protein, also known as human epidermal growth factor receptor 2 (HER2). When the Her-2/neu oncogene is amplified, the HER2 protein is overexpressed on the surface of cancer cells. This overexpression leads to increased signaling through the PI3K/AKT and MAPK pathways, promoting cell proliferation, survival, and angiogenesis. HER2 protein is a potent stimulator of cell growth, and its overexpression is associated with more aggressive tumor behavior.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because HER2 is not a glycoprotein. While it does interact with various proteins and signaling molecules, its primary structure is that of a receptor tyrosine kinase.

**Option B:** This option is incorrect because HER2 is not a hormone receptor. It is a member of the EGFR family and is activated by ligand binding, but it is not a receptor for steroid hormones like estrogen or progesterone.

**Option C:** This option is incorrect because HER2 is not a transcription factor. While it does regulate gene expression indirectly through its signaling pathways, it is not a protein that directly binds to DNA to regulate transcription.

**Option D:** This option is incorrect because HER2 is not a tumor suppressor protein. Its overexpression is associated with oncogenesis, and it promotes cell growth and survival rather than inhibiting these processes.

**Clinical Pearl / High-Yield Fact**
The HER2 status of a breast cancer is a critical prognostic factor and can influence treatment decisions. Patients with HER2-positive breast cancer may be eligible for targeted therapies like trastuzumab, which can improve outcomes and survival.

**Correct Answer: C. A 185-kDa transmembrane receptor tyrosine kinase.**

✓ Correct Answer: D. Receptor tyrosine kinase