**Core Concept:** Assessing the resectability of pancreatic cancer (CA Pancres) is crucial for determining the best treatment options for patients. Resectability refers to the ability to remove the tumor and surrounding healthy tissue without compromising vital organ function or causing excessive blood loss. The choice of investigations depends on the suspected pancreatic tumor location and size.

**Why the Correct Answer is Right:**

**Option C:** Abdominal CT scan is essential in evaluating the resectability of a pancreatic tumor. It provides detailed anatomy of the tumor, surrounding vasculature, and nearby organs. It helps in assessing the tumor size, location, and relationship to adjacent structures. However, CT scans may not always clearly demonstrate the tumor's relationship to blood vessels, nerves, and organs, which is crucial for determining resectability.

**Why Each Wrong Option is Incorrect:**

**Option A:** Ultrasound is limited in evaluating pancreatic tumors due to its low sensitivity for detecting tumors smaller than 2 cm and its limited ability to visualize the surrounding vasculature and organs.

**Option B:** PET-CT (Positron Emission Tomography-Computed Tomography) is primarily used for detecting cancerous lesions and assessing their glucose utilization. While it can identify primary pancreatic tumors and distant spread, it lacks information regarding tumor relation to adjacent structures and blood vessels, which is crucial for resectability assessment.

**Option D:** Endoscopy is primarily used for visualizing the gastrointestinal tract and its lesions. It provides limited information about pancreatic tumors and their relationship to adjacent structures and blood vessels, which is vital for resectability assessment.

**Clinical Pearl:**

In the case of suspected pancreatic cancer, a combination of techniques is often used to evaluate resectability. This may include abdominal CT scan, MRI (Magnetic Resonance Imaging), and in some cases, a selective angiography to visualize blood vessels and their relation to the tumor. This comprehensive approach helps ensure a thorough assessment of resectability and guides the most suitable therapeutic strategy for the patient.

Remember, the ultimate goal is to determine if the tumor is resectable, borderline resectable, or unresectable, and guide the subsequent treatment plan accordingly.