This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroid and adrenal glands, Subject name: Surgery
A 20 years old male presents with chronic constipation, headache and Marfanoid habitus, neuromas of tongue, medullated corneal nerve fibers and nodule of 2x2 cm size in the left lobe of thyroid. The most probable diagnosis is: 
Select and explain. 
A. Sporadic medullary carcinoma of thyroid, B. Familial medullary carcinoma of thyroid, C. MEN 2A, D. MEN 2B
D: MEN 2B
Answer: D: MEN 2B 
Explanation: - 2x2cm size of nodule most commonly medullary thyroid carcinoma - Headache because of pheochromocytoma - Therefore, diagnosis is MEN-2B MEN-2B Also known as MEN-3 Gene mutated is tyrosine kinase codon of RET oncogene. Pheochromocytoma M - MTC (most aggressive) M - marfanoid features M - mucosal neuromas. RET oncogene (tyrosine kinase domain) Autosomal dominant