Squamous cell carcinoma in serous effusions: Avoiding pitfalls in this rare encounter

Area of Science:

• Oncology
• Pathology
• Cytology

Background:

• Precise tumor classification is crucial for personalized medicine.
• Squamous cell carcinoma (SCC) is infrequently detected in serous effusions.
• SCC shares morphologic and immunohistochemical (IHC) similarities with other neoplasms, complicating diagnosis.

Purpose of the Study:

• To evaluate the diagnostic accuracy of SCC in serous effusions.
• To compare the effectiveness of cytology smears versus cellblocks with IHC.
• To identify reliable IHC markers for SCC identification in effusions.

Main Methods:

• A 17-year retrospective review of 49 effusion samples from 26 patients with SCC.
• Analysis of diagnostic accuracy based on specimen type (smears vs. cellblocks).
• Evaluation of various IHC markers, including p63, p40, Ber EP4, MOC 31, and mucin stains.

Main Results:

• SCC was most common in pleural fluid (84%), primarily lung (65%) and head/neck (16%).
• Cellblocks yielded more accurate SCC diagnoses than smears (P=.0005).
• p40 and p63 were the most specific IHC markers for SCC; mucin stains were helpful.
• Misclassifications, including false negatives/positives, occurred predominantly on cytology smears.

Conclusions:

• Cellblock preparation combined with appropriate IHC is essential for accurate SCC diagnosis in effusions.
• Cytology smears are prone to misclassification, especially distinguishing SCC from adenocarcinoma.
• Utilizing specific IHC markers like p40 and p63 improves diagnostic certainty.