p63 immunostaining in destained bronchoscopic cytological specimens

Area of Science:

• Pulmonary Pathology
• Cancer Biomarkers
• Immunohistochemistry

Background:

• p63 is a key regulatory protein in squamous cells, expressed in squamous carcinomas but typically absent in small-cell carcinomas (SCCs).
• Distinguishing SCCs from poorly differentiated squamous cell carcinoma of the lung (PDSLC) is crucial for appropriate patient management.
• Cytological smears are often the only available sample, posing challenges for traditional diagnostic methods.

Purpose of the Study:

• To evaluate the utility of p63 immunostaining in destained cytological slides for differentiating pulmonary squamous cell carcinoma from small-cell carcinoma.
• To establish reliable criteria for interpreting p63 staining in destained specimens.

Main Methods:

• Archival alcohol-fixed cytological smears from 60 pulmonary malignancies were destained, postfixed in formalin, and immunostained for p63.
• Citrate-based antigen retrieval and a streptavidin-biotin immunoperoxidase kit were employed.
• Normal cells (ciliated, goblet, reserve) and various tumor types (squamous cell carcinoma, SCC, PDSLC, adenocarcinoma) were analyzed for p63 expression.

Main Results:

• Postfixation in 10% formalin was essential for successful immunostaining.
• Squamous cell carcinomas were consistently p63 positive; reserve cells served as internal positive controls.
• Of 10 initially diagnosed SCCs, 4 were p63 positive, leading to reclassification of 3 into PDSLC after careful review.
• Adenocarcinomas, large-cell carcinomas, and metastatic adenocarcinomas were p63 negative.

Conclusions:

• p63 immunostaining in destained cytological slides is a valuable tool for differentiating PDSLC from SCC.
• Careful interpretation, considering internal controls and cytological features, is crucial for accurate diagnosis.
• This technique enhances diagnostic capabilities when dealing with limited or challenging cytological samples.