PAX immunoreactivity identifies alveolar rhabdomyosarcoma

Area of Science:

• Oncology
• Molecular Pathology
• Pediatric Pathology

Background:

• PAX5, a paired box transcription factor, is crucial in development and expressed in B-cell malignancies.
• PAX5 expression is also noted in various other tumors, prompting investigation as a diagnostic marker.
• Pediatric small round blue cell tumors represent a diverse group requiring accurate diagnostic tools.

Purpose of the Study:

• To evaluate PAX5 as a diagnostic marker for pediatric small round blue cell tumors.
• To assess PAX5 immunoreactivity across a spectrum of these tumors, including rhabdomyosarcoma subtypes.

Main Methods:

• Immunohistochemical staining for PAX5 was performed on a tissue microarray of pediatric tumors.
• Tumor types included embryonal rhabdomyosarcoma, alveolar rhabdomyosarcoma (ARMS), neuroblastoma, Wilms tumor, and others.
• Immunoreactivity was scored semiquantitatively, and genetic data for ARMS cases were analyzed.

Main Results:

• PAX5 was strongly expressed in all B-cell lymphoblastic lymphomas.
• Variable PAX5 staining was observed in Wilms tumors, predominantly in the epithelial component.
• 67% of ARMS cases showed PAX5 immunoreactivity, while embryonal rhabdomyosarcoma did not stain. PAX5 positivity in ARMS correlated with the presence of characteristic translocations.
• No other tumor types evaluated showed PAX5 immunoreactivity.

Conclusions:

• PAX5 is a sensitive marker for B-cell lymphoblastic lymphoma and a potential marker for Wilms tumors.
• PAX5 immunoreactivity may be specific for translocation-positive alveolar rhabdomyosarcoma (ARMS).
• Further studies are needed to confirm the diagnostic utility of PAX5 in ARMS.