**Core Concept**
The typical form of carcinoid syndrome is characterized by flushing, diarrhea, wheezing, and heart valvular abnormalities, resulting from the release of serotonin (5-HT) and other vasoactive substances by tumor cells into the systemic circulation.

**Why the Correct Answer is Right**
The correct answer is associated with the most frequent cause of carcinoid syndrome, which is the release of serotonin (5-HT) by tumor cells into the systemic circulation. This leads to the characteristic symptoms of the typical form of the syndrome. The liver, which normally metabolizes serotonin, is bypassed in metastatic carcinoid disease, allowing the high levels of serotonin to cause its effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Bronchial carcinoids are more commonly associated with atypical carcinoid syndrome, which presents with abdominal symptoms like pain and bleeding, rather than the typical symptoms.
**Option B:** Gastric carcinoids are more commonly associated with Zollinger-Ellison syndrome, which presents with severe peptic ulcer disease and diarrhea.
**Option C:** Pancreatic neuroendocrine tumors (PNETs) are more commonly associated with other syndromes like insulinoma or gastrinoma, rather than carcinoid syndrome.

**Clinical Pearl / High-Yield Fact**
The carcinoid syndrome is a classic example of a paraneoplastic syndrome, where the tumor releases substances that cause systemic symptoms, rather than local invasion or metastasis.

**Correct Answer:** C.