# Malignant pleural effusion due to metastatic squamous cell carcinoma exhibiting pseudoglandular and signet ring-like features: a case report

## TL;DR

A rare case of metastatic squamous cell carcinoma causing pleural effusion with unusual features is reported, highlighting the importance of accurate diagnosis for proper treatment.

## Contribution

The paper presents a rare case of metastatic squamous cell carcinoma in pleural effusion with pseudoglandular and signet ring-like features, emphasizing diagnostic challenges.

## Key findings

- Metastatic squamous cell carcinoma in pleural effusion can exhibit pseudoglandular and signet ring-like features, complicating diagnosis.
- Accurate cytopathological diagnosis is crucial for guiding clinical management in such cases.
- The patient's pleural effusion was confirmed as metastatic squamous cell carcinoma via cytological examination.

## Abstract

Malignant pleural effusion due to metastatic squamous cell carcinoma is uncommon. Keratinizing squamous cell carcinoma is morphologically identifiable, whereas nonkeratinizing squamous cell carcinoma poses diagnostic challenges and is prone to underdiagnosis or misdiagnosis.

This study reports the case of a 66-year-old East Asian man with a history of esophageal squamous cell carcinoma who developed pleural metastasis 3 years after chemotherapy, presenting with persistent, dull right-sided chest pain of unknown origin. Chest computed tomography revealed a large left pleural effusion with partial atelectasis. Approximately 600 ml of bloody fluid was drained via thoracentesis and catheter drainage. Cytological examination showed tumor cells exhibiting ring-like and pseudoglandular structure. The final cytological diagnosis was metastatic squamous cell carcinoma within the pleural effusion. The patient opted for symptomatic and conservative management and died 9 months after malignant pleural effusion diagnosis during follow-up.

When metastatic squamous cell carcinoma in pleural effusion is poorly differentiated and exhibits atypical changes such as pseudoglandular and signet ring-like features, vigilance is required during serous fluid cytopathological diagnosis. An accurate diagnosis provides the basis for subsequent clinical treatment.