The most common presenting symptom of pancreatic cancer, especially when located in the head of the pancreas, is painless jaundice. This occurs due to obstruction of the common bile duct by the tumor, leading to bile accumulation and subsequent jaundice without pain. Unlike other causes of jaundice, the absence of pain helps differentiate pancreatic cancer. Early detection based on this symptom is critical as it guides surgical intervention, often requiring a Whipple procedure for tumors in the pancreatic head. Hematemesis, severe diarrhea, and palpable masses are less common initial findings in pancreatic cancer.

Reference: Sabiston Textbook of Surgery, 21st Edition.