Metastatic papillary thyroid carcinoma in pleural effusion: a case report and review of the literature.

Introduction: Papillary thyroid carcinoma accounts for the most common type of thyroid cancer of well-differentiated type. Papillary thyroid carcinoma is featured by biologically low-grade and less aggressive tumors with a survival rate of 10 years in most of the diagnosed cases. Papillary thyroid carcinoma can be presented with the involvement of cervical lymph nodes in about 50% of the patients, yet distant spread is very uncommon.

Case Presentation: Herein, we discuss a Saudi male patient in his early 50s with a history of papillary thyroid carcinoma who presented to the emergency department complaining of shortness of breath and a radiological finding of hydrothorax. Cytologic examination together with immune-histochemical staining and molecular studies of pleural effusion aspiration concluded the definitive diagnosis of metastatic papillary thyroid carcinoma in the pleural space.

Conclusions: Papillary thyroid carcinoma seldom causes metastatic niches in the pleural space; this is a rare clinical presentation, nevertheless, a differential diagnosis of thyroid metastasis needs to be excluded. A definitive diagnosis of metastatic papillary thyroid carcinoma can be made using clinical presentation, cytologic examination, immunohistochemical investigation, and molecular testing. The most common mutation found in papillary thyroid carcinoma cases is the V600E mutation found in the BRAF gene, yet these patients have a relatively low probability of cancer recurrence. Patients with papillary thyroid carcinoma who have the BRAF mutation frequently experience metastases and relapses of the disease after the cancer has progressed aggressively. To help with therapy planning and the introduction of BRAF inhibitors, genetic testing for BRAF mutation may therefore prove to be a useful tool, especially in cases of aggressive subtypes of TC.