Primary renal sarcoma with SS18::POU5F1 gene fusion

Area of Science:

• Oncology
• Genetics
• Pathology

Background:

• Primary renal sarcomas are rare malignant neoplasms originating from the kidney's connective tissues.
• Undifferentiated sarcomas represent a heterogeneous group of tumors lacking specific differentiation.
• The SS18::POU5F1 gene fusion has been identified in specific soft tissue sarcomas, but its occurrence in primary renal tumors is novel.

Observation:

• A 38-year-old male presented with a 5 cm renal tumor invading the adrenal gland and renal vein.
• Microscopic examination revealed a predominantly undifferentiated round cell morphology with rhabdoid and spindle cell components.
• Immunohistochemistry showed expression of S100 protein and epithelial markers (EMA, cytokeratin), suggesting a potential myoepithelial phenotype.

Findings:

• This case represents the first documented instance of a primary renal undifferentiated sarcoma harboring the SS18::POU5F1 gene fusion.
• The tumor exhibited morphological and immunophenotypical features that overlap with other sarcoma subtypes.
• The presence of the SS18::POU5F1 fusion provides a specific molecular marker for this entity.

Implications:

• This finding expands the spectrum of soft tissue sarcomas associated with the SS18::POU5F1 gene fusion.
• It underscores the importance of molecular genetic testing in the accurate diagnosis of challenging renal neoplasms.
• Accurate diagnosis is critical for appropriate treatment and prognostic assessment of patients with rare renal sarcomas.