Immunocytochemistry of effusion fluids: Introduction to SCIP approach

Area of Science:

• Cytopathology
• Immunohistochemistry
• Oncology

Background:

• Cytomorphology of effusion fluids can be ambiguous, with reactive mesothelial cells and well-differentiated adenocarcinomas showing overlapping features.
• Malignant effusions, particularly from adenocarcinomas and diffuse malignant epithelioid mesothelioma, often lack definitive cytomorphologic signs of malignancy.
• Accurate interpretation is influenced by interpreter experience, patient demographics, and technical processing quality.

Purpose of the Study:

• To address the diagnostic challenges in effusion fluid cytology.
• To highlight the utility of immunocytochemistry as an adjunct diagnostic tool.
• To propose a refined methodology for immunocytochemical analysis of effusion fluids.

Main Methods:

• Application of immunocytochemistry on formalin-fixed cell-block sections is critical.
• Development of a fundamental immunopanel to map mesothelial and inflammatory cells in reactive effusions.
• Utilizing the subtractive coordinate immunoreactivity pattern (SCIP) approach for identifying and characterizing abnormal cell populations.

Main Results:

• Immunocytochemistry, when applied correctly to formalin-fixed cell blocks, significantly enhances diagnostic objectivity.
• A foundational immunopanel effectively establishes a baseline for identifying atypical cells.
• The SCIP approach facilitates the characterization of 'second-foreign' cell populations within effusion fluids.

Conclusions:

• Standardizing immunocytochemistry protocols for effusion fluids, particularly using formalin-fixed cell blocks, is essential for reliable results.
• Modified interpretation criteria may be necessary for challenging effusion fluid cases.
• The proposed immunopanel and SCIP method offer a structured approach to improve diagnostic accuracy in effusion cytology.