# CA19-9 producing locally advanced papillary thyroid carcinoma: a case report

## TL;DR

A rare case of locally advanced papillary thyroid carcinoma producing the tumor marker CA19-9 is reported, highlighting its potential as a diagnostic clue.

## Contribution

This is the first reported case of CA19-9 production in locally advanced papillary thyroid carcinoma.

## Key findings

- CA19-9 was detected in the serum and expressed in cancer cells of a locally advanced papillary thyroid carcinoma.
- Post-surgery, the patient's CA19-9 levels returned to normal, suggesting a direct link between the tumor and marker production.

## Abstract

CA19-9 is a tumor marker for gastrointestinal and biliary-pancreatic adenocarcinomas; however, its association with thyroid cancer is unknown. Here, we report a case of CA19-9 producing locally advanced papillary thyroid carcinoma (PTC).

A 66-year-old woman who was identified with a thyroid tumor after a close examination of an elevated serum CA19-9 level, which was detected at health screening, was referred to our hospital. Ultrasonography revealed a 34 × 31 mm hypoechoic lesion in the lower pole of the left thyroid lobe. Computed tomography revealed a solid thyroid tumor with tracheal invasion without any distant metastases. Bronchoscopy revealed tumor exposure into the tracheal lumen on the left side of the trachea. Fine-needle aspiration cytology led to a diagnosis of papillary thyroid carcinoma (PTC). The patient underwent a total thyroidectomy, tracheal sleeve resection with end-to-end anastomosis, and lymph node dissection in the left cervical and superior mediastinal regions (D3c) with a reversed T-shaped upper sternotomy down to the third intercostal level. Histopathological analysis confirmed the diagnosis of PTC with tracheal invasion and no lymph node metastases (pT4a Ex2 N0). Immunohistochemical staining showed the expression of CA19-9 in cancer cells. Postoperatively, the serum CA19-9 level of the patient decreased to within the normal range.

Some PTCs produce CA19-9, although less frequently. When elevated serum CA19-9 levels are observed, PTC should be included in the differential diagnosis for further investigation.