**Core Concept**
The question tests the student's knowledge of the molecular pathogenesis of pancreatic cancer, specifically the most frequently altered **oncogene**. Pancreatic cancer is a complex disease involving multiple genetic alterations.

**Why the Correct Answer is Right**
The **KRAS** oncogene is the most frequently altered in pancreatic cancer, with mutations found in up to 90% of cases. These mutations lead to constitutive activation of the **KRAS** protein, which in turn activates downstream signaling pathways involved in cell proliferation, survival, and migration.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while other oncogenes may be involved, they are not as frequently altered as **KRAS**.
**Option B:** Incorrect as tumor suppressor genes, not this specific option, are often inactivated in pancreatic cancer.
**Option D:** Incorrect because, although involved in other cancers, it is not the most frequently altered oncogene in pancreatic cancer.

**Clinical Pearl / High-Yield Fact**
Remember that **KRAS** mutations are an early event in pancreatic carcinogenesis, making them a potential target for early detection and therapy.

**Correct Answer:** D. KRAS