PAX8 Distinguishes Diffuse Large B-Cell Lymphoma Mimicking Sarcoma

Area of Science:

• Pathology
• Oncology
• Immunohistochemistry

Background:

• PAX8 is a transcription factor vital for the development of the thyroid, Müllerian system, and upper urinary/renal tract.
• PAX8 expression is observed in carcinomas originating from these sites.
• Polyclonal PAX8 antibody sensitivity and specificity have been evaluated in epithelial tumors and lymphomas.

Observation:

• PAX8 immunoreactivity was noted in a case initially diagnosed as unclassified high-grade sarcoma.
• The polyclonal PAX8 antibody can react with nonneoplastic B-cell lymphocytes, often used as positive internal controls.

Findings:

• The PAX8 staining was a key diagnostic indicator for revising the initial diagnosis.
• The tumor was reclassified as diffuse large B-cell lymphoma based on PAX8 expression and other markers.
• This highlights a potential pitfall of PAX8 immunoreactivity in diagnosing tumors.

Implications:

• PAX8 positivity in an epithelial cell marker-negative tumor warrants consideration of lymphoma in the differential diagnosis.
• Accurate diagnosis is crucial for appropriate patient treatment and management.
• This case underscores the importance of comprehensive diagnostic evaluation, including immunohistochemistry, in challenging cases.