# Metastatic Lung Adenocarcinoma Diagnosed by Thyroid Biopsy: A Case Report

## TL;DR

A rare case of lung cancer spreading to the thyroid was diagnosed through a thyroid biopsy during a tracheostomy in a 35-year-old woman.

## Contribution

This case report highlights the rare occurrence of metastatic lung adenocarcinoma diagnosed via thyroid biopsy.

## Key findings

- Lung cancer metastasis to the thyroid was confirmed through thyroid biopsy.
- The patient's symptoms and imaging findings led to the suspicion of malignancy.
- Prompt recognition of this rare condition is crucial for effective disease management.

## Abstract

Lung cancer metastasis to the thyroid gland is a rare occurrence. We report a rare presentation of metastatic lung adenocarcinoma diagnosed by thyroid biopsy during a tracheostomy in a 35-year-old female. A 35-year-old female with a history of epilepsy, hypothyroidism, and 15-pack-year smoking presented with four months of increasing neck swelling. The patient reported no airway symptoms upon admission. Initial flexible laryngoscopy revealed supraglottic edema. Workup including CT neck and chest revealed diffuse bilateral cervical lymphadenopathy, diffusely enlarged thyroid gland without any nodules or masses, and mediastinal lymphadenopathy with no obvious lung masses or nodules. Excisional right axillary nodal biopsy as well as right supraclavicular biopsy showed metastatic carcinoma with an equivocal staining pattern favoring lung adenocarcinoma versus thyroid carcinoma. During inpatient admission, the patient began having increasing dyspnea with flexible laryngoscopy revealing worsening supraglottic mucosal edema. The patient subsequently underwent tracheostomy with excisional thyroid biopsy due to concern for malignancy. Intraoperatively, the strap muscles were found to be firmly adhered to the underlying thyroid gland. Dissection of the thyroid isthmus revealed thickened tissue. The final pathology of the thyroid biopsy revealed metastatic adenocarcinoma, consistent with lung primary. It is important to keep in mind that, although rare, the thyroid gland may be a site of metastasis for primary lung adenocarcinoma. Prompt recognition and understanding of this possible event are key to achieving adequate disease control.