CEACAM5 and cancer: Medullary Thyroid Cancer (MTC) is a rare cancer of the thyroid parafollicular or ‘C’ cells, and is estimated to make up around 5–10% of all thyroid cancers.1 MTC was first described in 1906 by Jacquet as a thyroid tumour with amyloid, but the term MTC and its histological description of a solid non-follicular tumour with amyloid features was coined by Hazard et al., in 1959.2,3 Parafollicular C cells originate from the neural crest and so in keeping with their neuroendocrine origin, MTC secretes calcitonin (Ct), serotonin, chromogranin A and expresses carcinoembryonic antigen (CEA).