# Carcinoembryonic Antigen: Beyond a Gastrointestinal Tumour Marker

## TL;DR

This case report shows that elevated CEA levels can indicate medullary thyroid carcinoma, not just gastrointestinal cancers, emphasizing the need for broader evaluation.

## Contribution

The report highlights medullary thyroid carcinoma as a cause of elevated CEA, expanding its clinical relevance beyond GI malignancies.

## Key findings

- Elevated CEA levels can be associated with medullary thyroid carcinoma.
- A negative gastrointestinal evaluation should not rule out other CEA-related cancers.
- Genetic testing confirmed hereditary medullary thyroid carcinoma in the patient.

## Abstract

Carcinoembryonic antigen (CEA) is a widely used, non-specific tumour marker for gastrointestinal (GI) malignancies, particularly colorectal cancer (CRC). However, it can also be elevated in non-GI tumours and benign conditions, which are often overlooked.

A 60-year-old, asymptomatic man was referred for assessment of GI malignancy. During a health screening check, he was found to have a markedly elevated CEA, 121.8 ng/mL (reference range: <5.0 ng/mL). His family history included CRC, breast, and thyroid cancers. GI evaluation, which included a colonoscopy and gastroscopy, identified only a small sigmoid polyp and Helicobacter pylori gastritis. A pan-computed tomography (CT) scan showed a left thyroid nodule. He had fine-needle aspiration biopsies of the thyroid nodule on two occasions, and both were negative for malignancy. Serum calcitonin was markedly elevated. Following a discussion, the patient underwent total thyroidectomy, which confirmed multifocal medullary thyroid carcinoma (MTC). Postoperatively, the serum CEA declined and normalised after four months. Genetic testing revealed a germline RET mutation, establishing hereditary MTC. CEA elevation is commonly evaluated for GI malignancies.

This case report highlights that MTC is also associated with elevated CEA. Therefore, this should be assessed when GI evaluations are negative, to avoid delay in diagnosis.