# A Case of Concomitant Lung Adenocarcinoma and Pleural Metastasis of Papillary Thyroid Carcinoma With BRAF V600E Mutation

## TL;DR

A rare case is reported where a patient had two cancers, lung and thyroid, both with a specific BRAF mutation, and responded to targeted therapy.

## Contribution

This is the first reported case of concomitant BRAF V600E-mutated lung cancer and thyroid cancer metastasis.

## Key findings

- Both the lung and pleural tumor lesions had BRAF V600E mutations.
- Treatment with dabrafenib and trametinib reduced both tumor lesions.
- This case highlights the possibility of dual cancer diagnoses with shared mutations.

## Abstract

A 62‐year‐old woman with a history of papillary thyroid carcinoma presented to our hospital with fever and cough and was diagnosed with stage IV non‐small cell lung carcinoma (NSCLC). One year after chemoimmunotherapy, a re‐biopsy of the left pleural tumour lesion was performed. Histological analysis revealed papillary thyroid carcinoma. Another biopsy was performed on the primary tumour, and the histological analysis of the primary tumour lesion confirmed NSCLC. BRAF V600E mutations were detected in both left pleural metastatic lesions of papillary thyroid carcinoma and the primary tumour of NSCLC. Dabrafenib and trametinib reduced both tumour lesions. Here, we report a rare case of concomitant BRAF V600E‐mutated NSCLC and pleural metastasis from papillary thyroid carcinoma.

Recent molecular characterizations of multiple cancers have enabled the identification of driver oncogenes, and multiple molecular‐targeted inhibitors have been developed. We report the first case, to our knowledge, of concomitant lung carcinoma and pleural metastasis of papillary thyroid carcinoma with BRAF V600E mutation.