Note the Nodes: evaluation of staging procedures and treatment of pediatric extremity rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is the most common soft tissue tumor in children. It is a high-grade soft tissue tumor of mesenchymal origin. Lymph node metastases negatively affect prognosis and are relatively common in primary tumors of the extremities. This dissertation focusses on staging of these patients, its influence on treatment and prognosis, and the possibility of improving staging.
In recent years, 18F-FDG-PET/CT is increasingly performed as an adjunct to regular imaging (ultrasound, MRI, CT). In patients staged with an 18F-FDG-PET/CT, lymph node metastases were found more frequently (probably due to detection of lymph nodes at less common localizations such as in transit metastases (ITM)). A biopsy of the lymph nodes changed the lymph node stage in 15% of patients.
ITM are metastases located between the primary tumor and the first regional lymph node station. In RMS distal to the knee and elbow, ITM were identified in 17.5% of patients, in over 50% of N1 patients. Patients with both ITM and proximal regional nodal involvement had significantly worse prognosis than patients with lymph nodes in 1 lymph node station. Thus, it is important for surgeons to know which lymph nodes to biopsy.
In Chapters 5 and 6, we showed that the sentinel lymph node procedure is a feasible and accurate technique in RMS, and the pilot study using ICG as a tracer instead of patent blue showed promising results (Chapter 7). Because of small patient numbers, international collaboration is needed to draw conclusions from the available data. Chapter 8 is a consensus document on behalf of the International Soft Tissue Sarcoma Consortium (INSTRuCT) to create a standard for diagnosis, staging and treatment of patients with extremity RMS. This will allow comparison of data for further research in the future.