Increased 18F-FDG Avidity on PET/CT During Treatment for Rhabdomyosarcoma Confirmed to Be Mature Rhabdomyoblasts

Area of Science:

• Oncology
• Nuclear Medicine
• Pediatric Oncology

Background:

• 18F-FDG-PET is valuable for rhabdomyosarcoma staging.
• Its role in predicting outcomes and disease surveillance remains debated.
• Rhabdomyosarcoma is a common soft tissue sarcoma in children.

Purpose of the Study:

• To report a case of a suspicious 18F-FDG-PET finding in rhabdomyosarcoma.
• To investigate the nature of a new 18F-FDG-PET avid focus within a previous radiation field.
• To determine the clinical significance of this finding in the context of ongoing treatment.

Main Methods:

• Case report of an adolescent with metastatic fusion-positive rhabdomyosarcoma.
• Utilized 18F-FDG-PET imaging to monitor disease.
• Surgical resection of the suspicious lesion for histopathological analysis.

Main Results:

• An 18F-FDG-PET avid focus appeared in the primary tumor's radiation field during therapy.
• The standardized uptake value (SUV) of this focus increased, raising concerns for disease progression.
• Histopathology revealed the lesion to be terminally cytodifferentiated (mature) rhabdomyoblasts, not viable tumor.

Conclusions:

• The suspicious 18F-FDG-PET finding represented benign, mature rhabdomyoblasts.
• This case underscores the need for histopathological correlation of 18F-FDG-PET findings, especially in radiation fields.
• The patient achieved long-term remission following surgical resection of the lesion.