Elevated CEA in a Breast Cancer Patient with Overlooked Mixed Medullary-Papillary Thyroid Carcinoma

Carcinoembryonic antigen (CEA) is a tumor marker commonly associated with gastrointestinal and breast malignancy. For patients with persistent elevated CEA, a series of examinations should be performed in order to find a possible underlying occult malignancy that may not be clinically apparent. However, high CEA levels can also be found in benign conditions. We present a patient with persistently elevated CEA after breast cancer surgery and chemotherapy. Following an extensive survey, an overlooked mixed medullary-papillary thyroid carcinoma was identified as the cause of the elevated CEA, which was successfully treated with surgery. For patients with an elevated CEA, a tumor of neuroendocrine origin should be considered, such as medullary thyroid cancer (MTC). In order to facilitate accurate diagnosis, an FDG-PET scan may be an ideal tool to detect occult MTC.