This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
A 15 year old boy with cystic fibrosis presents with a 3-6kg weight loss over the past month unaccompanied by changes in his pulmonary and gastrointestinal symptoms. You suspect that he has developed which of the following? 
Select and explain. 
A. Bronchogenic carcinoma, B. Eating disorder, C. Biliary cirrhosis, D. Diabetes mellitus
D: Diabetes mellitus
Answer: D: Diabetes mellitus 
Explanation: Diabetes mellitus is a common development in the adolescent and older patient with cystic fibrosis. It results from pancreatic fibrosis and beta-cell destruction. It behaves like maturity onset diabetes, with little tendency to ketoacidosis. Diabetes should always be considered when an older child with cystic fibrosis loses weight.