**Core Concept**
Neuroendocrine tumors (NETs) of the pancreas are rare, hormone-secreting tumors that arise from the pancreatic islet cells. These tumors can cause a variety of symptoms depending on the hormone they secrete.

**Why the Correct Answer is Right**
Diarrhea is not the most common symptom of gastrinoma, a type of NET that secretes gastrin hormone. Gastrinomas typically cause peptic ulcers and abdominal pain due to excessive acid production in the stomach. Diarrhea is more commonly associated with VIPomas, which secrete vasoactive intestinal peptide (VIP) hormone. VIPomas cause a syndrome characterized by massive diarrhea, hypokalemia, and achlorhydria.

**Why Each Wrong Option is Incorrect**
**Option A:** Insulinoma is indeed the most common type of pancreatic NET, accounting for about 50% of all pancreatic NETs. Insulinomas secrete excess insulin, leading to hypoglycemia.
**Option B:** VIPomas, not gastrinomas, cause diarrhea due to the secretion of vasoactive intestinal peptide (VIP) hormone.
**Option D:** Somatostatinomas can cause gallstone formation due to the inhibition of cholecystokinin release, leading to decreased gallbladder contraction and bile stasis.

**Clinical Pearl / High-Yield Fact**
Gastrinomas are often associated with multiple endocrine neoplasia type 1 (MEN1) syndrome, a rare genetic disorder that affects multiple endocrine glands.

**✓ Correct Answer:** C. Diarrhea is MC symptom of gastrinoma