**Core Concept**
Growth promoting oncogenes are genes that encode proteins that promote cell growth and proliferation. When these genes become mutated or overexpressed, they can contribute to cancer development by driving uncontrolled cell growth.

**Why the Correct Answer is Right**
The correct answer is a gene that does not fit with the others in promoting cell growth. The other options (A, B, and C) are known to be growth-promoting oncogenes, often involved in signaling pathways that regulate cell growth and division. For example, **HER2** (Human Epidermal growth factor Receptor 2) is an oncogene that promotes cell growth by signaling for increased proliferation.

**Why Each Wrong Option is Incorrect**
**Option A:** **HER2** is a growth-promoting oncogene involved in signaling pathways that regulate cell growth and division. It is often overexpressed in certain types of breast cancer, leading to uncontrolled cell growth.
**Option B:** **HER1** (also known as **EGFR**, Epidermal Growth Factor Receptor) is a growth-promoting oncogene that signals for increased cell proliferation. It is often overexpressed in various types of cancer, including lung, breast, and colon cancer.
**Option C:** **HER3** is another growth-promoting oncogene involved in signaling pathways that regulate cell growth and division. It often forms heterodimers with **HER2**, amplifying its growth-promoting effects.

**Clinical Pearl / High-Yield Fact**
Growth-promoting oncogenes like **HER2**, **HER1**, and **HER3** are often targeted by specific therapies, such as monoclonal antibodies or tyrosine kinase inhibitors, to inhibit their growth-promoting effects and slow down cancer progression.

**Correct Answer: A. HER2 is a growth-promoting oncogene involved in signaling pathways that regulate cell growth and division.**