**Core Concept**
The pancreas is a complex organ with both exocrine and endocrine functions, and endocrine tumors can arise from the islet cells, which produce hormones such as insulin and glucagon. These tumors can be benign or malignant and are classified into different types based on their cell of origin.

**Why the Correct Answer is Right**
The most common endocrine tumor of the pancreas is a **Pancreatic Neuroendocrine Tumor (PNET)**, also known as a pancreatic islet cell tumor. PNETs arise from the alpha, beta, or delta cells of the islets of Langerhans and can produce excessive amounts of hormones such as insulin, gastrin, or vasoactive intestinal peptide (VIP). The beta-cell tumors, specifically, can produce excess insulin, leading to **Hyperinsulinemic Hypoglycemia**. PNETs are typically slow-growing and can be benign or malignant.

**Why Each Wrong Option is Incorrect**
**Option A:** **Glucagonoma** is a rare type of PNET that produces excess glucagon, causing hyperglycemia, but it is not the most common type.
**Option B:** **Somatostatinoma** is a rare type of PNET that produces excess somatostatin, leading to various symptoms, but it is not the most common type.
**Option C:** **VIPoma** is a rare type of PNET that produces excess VIP, causing severe diarrhea and dehydration, but it is not the most common type.

**Clinical Pearl / High-Yield Fact**
PNETs can present with a wide range of symptoms, including hormonal imbalances, abdominal pain, and gastrointestinal symptoms, and can be challenging to diagnose due to their rarity and nonspecific presentation.

**Correct Answer: C. Pancreatic Neuroendocrine Tumor (PNET)**