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: Medicine
Development of pellagra like skin lesion in carcinoid syndrome is due to: 
Select and explain. 
A. Inadequate conversion of Tryptophan to Niacin, B. Dietary Niacin deficiency, C. Serotonin induced skin rash mimicking pellagra, D. Paraneoplastic manifestation
A: Inadequate conversion of Tryptophan to Niacin
Answer: A: Inadequate conversion of Tryptophan to Niacin 
Explanation: One of the main secretory products of carcinoid tumors involved in the carcinoid syndrome is serotonin which is synthesized from tryptophan. Up to 50% of dietary tryptophan can be used in this synthetic pathway by tumor cells, and this can result in inadequate supplies for conversion to niacin; hence, some patients (2.5%) develop pellagra-like lesions. Reference: Harrisons Principles of Internal Medicine, 18th Edition, Page 3063