Cytological Diagnosis of Malignant Pleural Effusion Caused by Metastatic Squamous Cell Carcinoma: A Series of Four Cases

Abstract

The majority of malignant pleural effusions are caused by adenocarcinomas, with the most common primary sites being the lung and breast in men and women, respectively. Metastatic squamous cell carcinoma in serous effusions is rare, accounting for less than 3% of all malignant effusions. The most common primary site of origin for metastatic squamous cell carcinoma involving serous effusions is the lung, followed by the head and neck, oesophagus, and cervix. Well-differentiated squamous cell carcinoma in pleural effusion, characterised by keratinised cells with hyperchromatic nuclei, tadpole cells, and fiber cells, is exceedingly rare. Poorly differentiated squamous cell carcinomas often present a diagnostic challenge and can be mistaken for poorly differentiated adenocarcinoma, malignant mesothelioma, or reactive mesothelial hyperplasia. Immunohistochemistry is often required for a definitive diagnosis. Making an accurate diagnosis is crucial for providing optimal treatment to the patient. In this series, four cases (56 years old male,69 years old male, 60 years old female and 81 years old male) of malignant pleural effusion caused by metastatic squamous cell carcinoma arising from the lung, oropharynx, cervix, and oesophagus were examined. While one of the cases involved a well-differentiated squamous cell carcinoma with characteristic cellular morphology that allowed for a straightforward diagnosis, the other three cases were poorly differentiated squamous cell carcinomas that required cell block preparation and immunohistochemistry for confirmation.