Medullary Thyroid Cancer Discovered Through Elevated Carcinoembryonic Antigen Levels Post Colorectal Cancer Resection

Abstract

Medullary thyroid carcinoma (MTC) is a rare malignancy accounting for approximately 5% of all thyroid cancers. Common predictors of aggressiveness of MTC include specific RET mutations and levels of calcitonin. Carcinoembryonic antigen is a tumor marker that can also provide diagnostic and prognostic information. We present the case of a 53-year-old woman with persistently elevated carcinoembryonic antigen levels 2 months post–curative colorectal cancer (CRC) resection. She was found to have MTC by fine-needle biopsy, incidentally detected on full-body 18F-fluorodeoxyglucose–positron emission tomography while investigating colorectal cancer recurrence.