Medullary thyroid carcinoma with normal serum calcitonin and carcinoembryonic levels; a case with review of literature

•Medullary thyroid carcinoma (MTC) is a primary neuroendocrine tumor.•It is mostly associated with excessive calcitonin (CT) secretion.•CT is an accurate and sensitive biomarker for the diagnosis and post-operative follow up.•In very rare cases, pre-operative calcitonin level reported to be normal.•This is to report a rare case of MTC with normal serum calcitonin and carcinoembryonic level.