Immunohistochemical Labelling for Cyclo-oxygenase-2: Does the Positive Control Guarantee Standardized Results?

Area of Science:

• Veterinary Oncology
• Immunohistochemistry
• Molecular Diagnostics

Background:

• Cyclo-oxygenase-2 (COX-2) is a therapeutic target in veterinary oncology.
• Previous studies on COX-2 expression show heterogeneous results, hindering definitive conclusions.
• Reproducibility issues necessitate standardized controls in multi-laboratory studies.

Purpose of the Study:

• To assess the efficacy of a defined positive control in ensuring reproducible cyclo-oxygenase-2 (COX-2) expression analysis.
• To evaluate inter-laboratory and inter-reader variability in immunohistochemical assessment of COX-2 in veterinary tumors.
• To determine if renal macula densa positivity is a sufficient control for reliable COX-2 quantification.

Main Methods:

• Immunohistochemical labeling of cyclo-oxygenase-2 (COX-2) in 15 colorectal tumors and 15 oral squamous cell carcinomas.
• Six European laboratories participated, using a defined positive control (renal macula densa).
• Blinded evaluation of slides by three pathologists for percentage of positive cells and labeling intensity, followed by statistical analysis.

Main Results:

• Renal macula densa positivity proved insufficient to guarantee reproducible results for COX-2 percentage of positive cells and labeling intensity.
• Significant inter-reader variability was statistically confirmed among pathologists.
• The defined positive control failed to standardize COX-2 expression analysis across different laboratories.

Conclusions:

• Standard positive controls, such as renal macula densa, may not be adequate for ensuring reproducible COX-2 expression analysis in veterinary oncology.
• Significant inter-reader variability necessitates the adoption of automated quantitative evaluation techniques, like image analysis, to improve consistency and reliability.