**Core Concept**
The pancreas is a complex organ with both endocrine and exocrine functions, and cancer arising from its cells can have different locations within the organ. The most common site of pancreatic cancer is related to the ductal system, which is responsible for the production and secretion of digestive enzymes.

**Why the Correct Answer is Right**
The head of the pancreas is the most common site of pancreatic cancer, accounting for approximately 60-70% of all cases. This is due to the fact that the pancreatic duct, which is the main conduit for the secretion of digestive enzymes, is located in the head of the pancreas. The head of the pancreas also receives a higher blood supply, which may contribute to its increased susceptibility to cancer. The pancreatic ductal adenocarcinoma (PDAC) cells in the head of the pancreas often arise from the ductal epithelium, which is the lining of the pancreatic duct.

**Why Each Wrong Option is Incorrect**
**Option A:** The body of the pancreas is less common site for pancreatic cancer, but still accounts for a significant proportion of cases. However, it is not the most common site.
**Option B:** The tail of the pancreas is the least common site for pancreatic cancer, and is often associated with a better prognosis due to its easier accessibility for surgical resection.
**Option C:** The neck of the pancreas is a transitional zone between the head and the body, and is not a distinct site for pancreatic cancer.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the head of the pancreas is the most common site for pancreatic cancer, and that pancreatic cancer often presents with non-specific symptoms such as jaundice, weight loss, and abdominal pain.

**Correct Answer: C. Tail of the pancreas is the least common site of Ca pancreas.