With a serum calcitonin concentration of 7.4 pmol/L (reference <24 pmol/L) and a carcinoembryonic antigen (CEA) concentration of 3.3 μg/L (reference in non-smokers < 5.0 μg/L), medullary thyroid cancer became less likely. This evidence concerns the gene CEACAM5 and medullary thyroid gland carcinoma.