Rhabdomyosarcoma and pleomorphic sarcoma in the same location : Recurrence or new entity?

Area of Science:

• Oncology
• Radiation Oncology

Background:

• Soft tissue sarcomas (STS) are rare adult solid tumors with diverse risk factors including genetic predisposition and prior radiotherapy.
• Differential diagnoses for new swelling in STS patients include recurrence, secondary primary cancers, metastasis, and radiation-associated STS.

Observation:

• A 64-year-old male with pleomorphic rhabdomyosarcoma developed a painful swelling 5 years after initial resection and radiotherapy.
• Resected tissue revealed pleomorphic sarcoma (NOS); molecular analysis showed no specific fusions.
• The short latency and lack of specific features complicated the diagnosis.

Findings:

• The second sarcoma, lacking rhabdomyoblastic differentiation and occurring in a previously irradiated site, was diagnosed as radiation-associated STS.
• This diagnosis was supported by the low likelihood of a second primary in the same location.

Implications:

• This case highlights the diagnostic challenges of radiation-associated STS due to their non-specific features.
• Recognizing radiation-associated STS is critical to avoid further radiotherapy in compromised tissue.
• A short interval between initial treatment and a new sarcoma diagnosis should prompt thorough investigation beyond simple recurrence.