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: Surgery
After thyroidectomy for medullary carcinoma of thyroid, which is impoant for determining recurrence of tumour: September 2009 
Select and explain. 
A. Thyroglobulin, B. TSH, C. Carcinoembryonic antigen, D. Thyroxine levels
C: Carcinoembryonic antigen
Answer: C: Carcinoembryonic antigen 
Explanation: As. C: Carcinoembryonic antigenUnlike papillary and follicular thyroid cancers which arise from thyroid hormone producing cells, medullary cancer of the thyroid originates from the parafollicular cells (also called C cells) of the thyroid.These C cells make a different hormone called calcitonin.High levels of serum calcitonin and carcinoembryonic antigen are produced by many medullary tumours.Levels falls after resection and rise again with recurrence making it a valuable tumour marker in the follow-up of patients with this diseaseThis cancer has a much lower cure rate than does the "well differentiated" thyroid cancers (papillary and follicular), but cure rates are higher than they are for anaplastic thyroid cancer.