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What is The most common site for carcinoma of the pancreas - and explain in detail?
Pancreatic carcinoma 

Pancreatic carcinoma is the most common malignant tumor of pancrease.

Risk factors

Smoking → Most consistent risk factor.   
Chronic pancreatitis     
Obesity
High fat, low fibre diet.
Diabetes

Pathology

Pancreatic carcinoma are ductal adenocarcinomas.
The most common site is head of pancreas. The distribution is as follows.

Head (70%)
Body (20%)
Tail (10%)